Development of an updated assay for prekallikrein activator in albumin and immunoglobulin therapeutics.

BACKGROUND: Prekallikrein activator (PKA) is a contaminating enzyme found in therapeutic albumin and immunoglobulin products. The level is commonly measured using methods such as that defined by the European Pharmacopoeia (Ph Eur) with traceability to the WHO International Standard for PKA. This method generally works well, but problems are sometimes observed. MATERIALS AND METHODS: A simplified one-step method has been developed to replace the existing Ph Eur two-step method which consists of kallikrein generation followed by kallikrein measurement using a chromogenic substrate. Analysis of data from the one-stage method is simplified by the use of a dedicated online app. RESULTS: The one-stage method was validated against the current Ph Eur method using batches of albumin and immunoglobulins. Problem batches of immunoglobulins were investigated using the one-stage method. Improved methodology using true initial rate determinations and use of acid-treated prekallikrein substrate (PKS) helped understand and reduce artefactual results. CONCLUSIONS: The one-stage method and associated app streamline real-time determination of PKA and promote good principles of enzyme assays to limit substrate depletion, while also conserving expensive PKS. Blanking steps and reproducibility are simplified.

Contact system activation and high thrombin generation in hyperthyroidism.

BACKGROUND: Hyperthyroidism is associated with increased thrombotic risk. As contact system activation through formation of neutrophil extracellular traps (NET) has emerged as an important trigger of thrombosis, we hypothesized that the contact system is activated along with active NET formation in hyperthyroidism and that their markers correlate with disease severity. SUBJECTS AND METHODS: In 61 patients with hyperthyroidism and 40 normal controls, the levels of coagulation factors (fibrinogen, and factor VII, VIII, IX, XI and XII), D-dimer, thrombin generation assay (TGA) markers, NET formation markers (histone-DNA complex, double-stranded DNA and neutrophil elastase) and contact system markers (activated factor XII (XIIa), high-molecular-weight kininogen (HMWK), prekallikrein and bradykinin) were measured. RESULTS: Patients with hyperthyroidism showed higher levels of fibrinogen (median (interquartile range), 315 (280-344) vs 262 (223-300), P = 0.001), D-dimer (103.8 (64.8-151.5) vs 50.7 (37.4-76.0), P < 0.001), peak thrombin (131.9 (102.2-159.4) vs 31.6 (14.8-83.7), P < 0.001) and endogenous thrombin potential (649 (538-736) vs 367 (197-1147), P = 0.021) in TGA with 1 pM tissue factor, neutrophil elastase (1.10 (0.39-2.18) vs 0.23 (0.20-0.35), P < 0.001), factor XIIa (66.9 (52.8-87.0) vs 73.0 (57.1-86.6), P < 0.001), HMWK (6.11 (4.95-7.98) vs 3.83 (2.60-5.68), P < 0.001), prekallikrein (2.15 (1.00-6.36) vs 1.41 (0.63-2.22), P = 0.026) and bradykinin (152.4 (137.6-180.4) vs 118.3 (97.1-137.9), P < 0.001) than did normal controls. In age- and sex-adjusted logistic regression analysis, fibrinogen, factor VIII, IX and XIIa, D-dimer, peak thrombin, neutrophil elastase, HMWK and bradykinin showed significant odds ratios representing hyperthyroidism's contribution to coagulation and contact system activation. Free T4 was significantly correlated with factors VIII and IX, D-dimer, double-stranded DNA and bradykinin. CONCLUSION: This study demonstrated that contact system activation and abundant NET formation occurred in the high thrombin generation state in hyperthyroidism and were correlated with free T4 level.

Evidence of contact activation in patients suffering from ST-elevation myocardial infarction.

INTRODUCTION: Factor (F) XIIa is an attractive target for anticoagulation in arterial thrombosis. The aim of this study is to investigate the degree of involvement of the contact system in cardiac infarctions. METHODS AND PATIENTS: 165 patients suffering from ST-elevation myocardial infarction (STEMI) and 100 healthy controls were included in the study. Samples were drawn at admission before percutaneous intervention (PCI), 1-3days post-percutaneous intervention (PCI) and, in one-third of the patients, 3months after PCI. In order to investigate the degree of Factor XII (FXII) activation, changes in FXIIa/AT and FXIIa/C1INH complex levels were quantified by ELISA. RESULTS: FXIIa/AT levels at admission (0.89±0.50; p<0.01) were significantly higher than those in normal individuals (0.39±0.28), but the levels after 1-3days (0.33±0.33; p<0.05) were essentially normalized. In contrast, the FXII/C1INH levels at admission (1.40±0.72; p<0.001) and after 1-3days (0.83±0.59; p<0.001) were both significantly higher than those in normal individuals (0.40±0.30). FXIIa/AT and FXIIa/C1INH complexes at admission (p<0.001; p<0.001) and after 1-3days (p<0.02; p<0.001) were significantly different from those at 3months. No significant differences were observed when the data were stratified for patency (open/closed culprit lesions). CONCLUSION: Both FXIIa/AT and FXIIa/C1INH complexes were significantly increased and reflected the activation of FXII in STEMI patients at admission. In particular, FXIIa/AT complex elevations support the hypothesis that clot propagation-mediated FXII activation had occurred, and this activation may be a target for anticoagulation in patients with cardiac infarction. Based on previous studies, the FXIIa/C1INH complex levels were primarily interpreted to reflex endothelial cell activation.

Factor XII-mediated contact activation related to poor prognosis in disseminated intravascular coagulation.

BACKGROUND: The contact system that initiates the intrinsic coagulation pathway plays a role in thrombus formation. Since neutrophil extracellular traps (NET), which are mainly composed of histone and DNA, are actively formed in disseminated intravascular coagulation (DIC) and the NET can activate factor XII, it is plausible that a NET component strongly activates the contact system in patients with DIC. METHODS: In 146 patients suspected of having DIC, the plasma levels of contact system factors including factor XII, activated factor XII (XIIa), prekallikrein, high-molecular-weight kininogen (HMWK), bradykinin, extrinsic factor VII and histone­DNA complex were measured. In an in vitro plasma clotting assay, factor XII­deficient plasma was stimulated with silica or histone. RESULTS: The levels of not only extrinsic coagulation factor VII but also intrinsic coagulation factors including factors XI and XII were significantly decreased in patients with overt DIC in comparison with those with no overt DIC. Factor XIIa and histone-DNA complex were also significantly increased in patients with overt DIC. However,HMWK, prekallikrein and bradykin inw ere not significantly different between patients with and without overt DIC. Interestingly, factors XII and XIIa were revealed as significantly independent potential prognostic markers for DIC. The histone-DNA complex level significantly contributed to the factor XIIa level (20.6%). In an in vitro clotting assay, histone, a major component of NET, activated coagulation that was dependent, in part, on the presence of factor XII. CONCLUSION: These findings suggest that active NET formation can induce factor XII-mediated coagulation activation in patients with DIC with poor prognosis. The resulting factor XIIa release can be used as an independent potential prognostic marker for DIC. Activation of factor XII-mediated coagulation may be a potential therapeutic target in DIC,

Hypercoagulability and the risk of myocardial infarction and ischemic stroke in young women.

BACKGROUND: Myocardial infarction (MI) and ischemic stroke (IS) are acute forms of arterial thrombosis and share some, but not all, risk factors, indicating different pathophysiological mechanisms. OBJECTIVE: This study aims to determine if hypercoagulability has a differential effect on the risk of MI and IS. PATIENTS AND METHODS: We reviewed the results from the Risk of Arterial Thrombosis in Relation to Oral Contraceptives study, a population-based case-control study involving young women (< 50 years) with MI, non-cardioembolic IS and healthy controls. From these data, relative odds ratios (ORIS /ORMI ) and their corresponding confidence intervals for all prothrombotic factors that were studied in both subgroups were calculated. RESULTS: Twenty-nine prothrombotic risk factors were identified as measures of hypercoagulability. Twenty-two of these risk factors (21/29, 72%) had a relative odds ratios > 1; for 12 (41%), it was > 2; and for 5 (17%), it was > 2.75. The five risk factors with the largest differences in associations were high levels of activated factor XI (FXI) and FXII, kallikrein, the presence of lupus anticoagulans, and a genetic variation in the FXIII gene. CONCLUSION: In young women, prothrombotic factors are associated more with the risk of IS than with MI risk, suggesting a different role of hypercoagulability in the mechanism leading to these two diseases.

Heparan sulfate proteoglycans mediate factor XIIa binding to the cell surface.

Hageman factor (FXIIa) initiates the intrinsic coagulation pathway and triggers the kallikrein-kinin and the complement systems. In addition, it functions as a growth factor by expressing promitogenic activities toward several cell types. FXIIa binds to the cell surface via a number of structurally unrelated surface receptors; however, the underlying mechanisms are not yet fully understood. Here, we demonstrate that FXIIa utilizes cell membrane-bound glycosaminoglycans to interact with the cell surface of human lung fibroblasts (HLF). The combination of enzymatic, inhibitory, and overexpression approaches identified a heparan sulfate (HS) component of proteoglycans as an important determinant of the FXIIa binding capacity of HLF. Moreover, cell-free assays and competition experiments revealed preferential binding of FXIIa to HS and heparin over dextran sulfate, dermatan sulfate, and chondroitin sulfate A and C. Finally, we demonstrate that fibroblasts isolated from the lungs of the patients suffering from idiopathic pulmonary fibrosis (IPF) exhibit enhanced FXIIa binding capacity. Increased sulfation of HS resulting from elevated HS 6-O-sulfotransferase-1 expression in IPF HLF accounted, in part, for this phenomenon. Application of RNA interference technology and inhibitors of intracellular sulfation revealed the cooperative action of cell surface-associated HS and urokinase-type plasminogen activator receptor in the accumulation of FXIIa on the cell surface of IPF HLF. Moreover, FXIIa stimulated IPF HLF migration, which was abrogated by pretreatment of cells with heparinase I. Collectively, our study uncovers a novel role of HS-type glycosaminoglycans in a local accumulation of FXIIa on the cell membrane. The enhanced association of FXIIa with IPF HLF suggests its contribution to fibrogenesis.

Human plasma-derived immunoglobulin G fractionated by an aqueous two-phase system, caprylic acid precipitation, and membrane chromatography has a high purity level and is free of detectable in vitro thrombogenic activity.

BACKGROUND AND OBJECTIVES: Instituto Clodomiro Picado has developed an immunoglobulin G (IgG) plasma fractionation process combining a polyethylene glycol/phosphate aqueous two-phase system (ATPS), caprylic acid precipitation and anion-exchange membrane chromatography. We evaluated the purity and in vitro thrombogenicity of such IgG, in line with current international requirements. MATERIALS AND METHODS: Contributions of the different production steps to reduce thrombogenicity were assessed at 0·2 l-scale, and then the methodology was scaled-up to a 10 l-scale and final products (n = 3) were analysed. Purity, immunoglobulin composition, and subclass distribution were determined by electrophoretic and immunochemical methods. The in vitro thrombogenic potential was determined by a thrombin generation assay (TGA) using a Technothrombin fluorogenic substrate. Prekallikrein activator (PKA), plasmin, factor Xa, thrombin and thrombin-like activities were assessed using S-2302, S-2251, S-2222, S-2238 and S-2288 chromogenic substrates, respectively, and FXI by an ELISA. RESULTS: The thrombogenicity markers were reduced mostly during the ATPS step and were found to segregate mostly into the discarded liquid upper phase. The caprylic acid precipitation eliminated the residual procoagulant activity. The IgG preparations made from the 10 l-batches contained 100% gamma proteins, low residual IgA and undetectable IgM. The IgG subclass distribution was not substantially affected by the process. TGA and amidolytic activities revealed an undetectable in vitro thrombogenic risk and the absence of proteolytic enzymes in the final product. CONCLUSIONS: Fractionating human plasma by an ATPS combined with caprylic acid and membrane chromatography resulted in an IgG preparation of high purity and free of a detectable in vitro thrombogenic risk.

C1-esterase inhibitor treatment: preclinical safety aspects on the potential prothrombotic risk.

Human plasma-derived C1-esterase inhibitor (C1-INH) is an efficacious and safe treatment for hereditary angioedema. However, thrombotic events in subjects treated with C1-INH at recommended or off-label, high doses have been reported. In this study, we addressed the potential prothrombotic risk of C1-INH treatment in high doses using a non-clinical rabbit model. Following intravenous infusion of C1-INH to rabbits at doses up to 800 IU/kg, the exposure and the pharmacodynamic efficacy of C1-INH in rabbits were confirmed by activity measurements of C1-esterase, and coagulation factors XIa and XIIa, respectively. Potential prothrombotic effects were assessed following induction of venous and arterial thrombosis using in vivo models of venous and arterial stasis, complemented by various in vitro assays of coagulation markers. Administration of C1-INH at doses up to 800 IU/kg did not potentiate thrombus formation during venous stasis. In contrast, inhibition of arterial occlusion was observed upon C1-INH administration when compared with isotonic saline treatment, indicating antithrombotic rather than prothrombotic activity of high dose C1-INH treatment in vivo. This was further confirmed in vitro by decreased thrombin generation, increased activated partial thromboplastin time, clotting time and clot formation time, and inhibition of platelet aggregation. No relevant changes in fibrinolysis or in the levels of thrombin-antithrombin complexes, and prothrombin fragment 1+2 were observed upon high dose C1-INH treatment. The data suggest that treatment of healthy rabbits with high doses of C1-INH could potentially inhibit coagulation and thrombus formation rather than induce a prothrombotic risk.

Assessment of immunoglobulin concentrates on thrombogenic activity by thrombin generation assay, prekallikrein activator assay, and size-exclusion chromatography.

BACKGROUND: Immunoglobulin G (IgG) concentrates have recently been found to be contaminated with procoagulant impurities causing thromboembolic events (TEEs) in vivo. In this study the question was raised whether a thrombin generation assay (TGA) will be able to characterize IgG samples from the Austrian market with regard to their thrombogenic potential. STUDY DESIGN AND METHODS: A total of 44 IgG concentrates have been assayed by TGA employing pooled normal plasma and Factor (F)XI-deficient plasma (FXIdp). Furthermore, the prekallikrein activator assay including determination of blank values, size-exclusion chromatography, and further test systems required for batch release testing of IgG concentrates according to the European Pharmacopeia (Pharm. Eur.) were carried out. RESULTS: All samples complied with acceptance criteria stated in the Plarm. Eur. and/or prescribed by the marketing approval. One intravenous immunoglobulin (IVIG) involved in TEEs exceeded a threshold level of 350 nmol peak thrombin, which was not exceeded after change of manufacture and by all the other IVIGs tested. Two hyperimmune globulins revealed elevated peak thrombin levels of up to 810 nmol in FXI and up to 285 nmol in FXIdp. CONCLUSION: The study indicates that the TGA is able to reliably predict procoagulant activities probably associated with the presence of FXIa and potential thrombogenicity. Comparison of thrombin generation with product-specific acceptance criteria as well as variables from other test systems as amidolytic activity and molecular size can help to monitor IgG quality and manufacturing changes with regard to thrombogenicity.

A new enzyme-linked immunosorbent assay recognizing both rat and human activated coagulation Factor XII (FXIIa).

We describe the first sandwich enzyme-linked immunosorbent assay (ELISA) capable of recognizing both rat and human activated coagulation Factor XII (FXIIa). Increased plasma concentrations of FXIIa have been associated with adverse outcomes in several cardiovascular disease states. In humans, the FXIIa antigen in plasma is quantified by a direct sandwich ELISA employing an antibody (mAb 2/215) raised against its ß-fragment (ß-FXIIa), but this assay is unable to detect rat ß-FXIIa antigen. Thus, experimental models are at present limited in their capacity to reveal mechanisms by which FXIIa might contribute to cardiovascular pathology. Consistent with overlap between human and rat FXIIa protein epitope sequences, Western blot analysis and ELISA demonstrate that another previously developed antibody against human FXIIa (mAb 201/9) detects ß-FXIIa in both human and rat plasma, with no evidence for cross-reactivity with the FXII zymogen or FXIIa complexed with its endogenous inhibitor. The mAb 201/9 based ELISA identified similar elevations in FXIIa in plasma from rats and humans with chronic renal failure. The capacity of this ELISA to identify rat plasma FXIIa has potential application to a wide range of experimental models of human cardiovascular disease.

Identification of kallikrein and FXIa as impurities in therapeutic immunoglobulins: implications for the safety and control of intravenous blood products.

BACKGROUND AND OBJECTIVES: The occurrence of thromboembolic events (TEEs) with intravenous immunoglobulin lots (IVIGs) raised the question of the causative agent for these adverse events. We investigated the predominant plasma proteases in 19 IVIG lots from five manufacturers including three lots associated with adverse events. MATERIAL AND METHODS: The inhibitor profile of the amidolytic activity in IVIG lots was investigated with substrates S-2302 and S-2288. In immunocapture assays, prekallikrein and FXI antigen and respective active proteases were quantified. Non-activated partial thromboplastin time (NAPTT) and a modified FXIa PTT served as global and FXIa-specific clotting assays, respectively. RESULTS: Kallikrein was identified as one major contaminant activity in IVIGs. A second activity was seen in some IVIGs with substrate S-2288, but not with S-2302. Inhibition studies excluded FXIIa, thrombin or plasmin as contaminant activity. FXI antigen was seen in all 19 IVIG lots, and FXIa activity was found as second major impurity in some IVIGs, including all lots involved in TEEs. FXIa highly correlated with a short clotting time in NAPTT. CONCLUSIONS: Kallikrein and FXIa are the major contaminants in IVIGs. FXIa was highly procoagulant, with highest level in TEE-associated IVIGs. Since the NAPTT unambiguously identified FXIa procoagulant activity in IVIGs, its implementation as a release test would improve the safety of IVIGs.

A collaborative study to establish the 1st national standard of prekallikrein activator in Korea.

The aim of this study was to establish the first national standard for prekallikrein activator (PKA) calibrating to the first international standard PKA. A collaborative study among five laboratories, including three manufacturers and two national control laboratories, was carried out to evaluate the suitability of a candidate to serve as a national standard of PKA. The candidate was manufactured in GMP facility following approved human serum albumin fractionation procedure and freeze-dried 5% albumin solution containing PKA. Participants were provided with sufficient samples and asked to use lab-made prekallikrein substrate prepared in accordance with European Pharmacopeia and also to use a commercial prekallikrein provided as part of the study. The PKA concentration of the candidate was 61.8 IU per vial using lab-made prekallikrein. However, the concentration was 54.2 IU per vial using commercial prekallikrein. The variability obtained at each laboratory ranged from 1.9% to 5.1% for within-a-day and from 5.6% to 9.0% for day-to-day. The candidate showed excellent stability from accelerated degradation study and real-time stability study. As a conclusion, the candidate preparation was suitable to serve as a Korean National Standard for PKA.

Activated factor XII type A and B-type natriuretic peptide are complementary and incremental predictors of mortality in patients following admission with acute coronary syndrome.

The aim of this analysis was to assess the predictive value of activated factor XII type A (XIIaA) and B-type natriuretic peptide (BNP) in acute coronary syndrome patients stratified according to troponin release and to evaluate their complementary utility as predictors of all-cause mortality and recurrent troponin T (TnT)-positive events. Multivariable analysis in 870 patients admitted with suspected myocardial infarction was performed using the Cox proportional hazard ratio model. Variables in the model included XIIaA and BNP as well as conventional risk factors for mortality. Although both XIIaA and BNP were identified as independent predictors for all-cause mortality in the total group of patients, only BNP was found to be an independent predictor for all-cause mortality in patients with a confirmed myocardial infarction (TnT > 0.05 ng/ml) at admission (hazard ratio 4.24, 95% confidence interval 1.28-14.07), whereas only XIIaA was an independent predictor for all-cause mortality in patients with low TnT release (0.01 < TnT < or = 0.05 ng/ml) at admission (hazard ratio 10.37, 95% confidence interval 2.89-37.21). The combination of these two biomarkers provided complementary prognostic information for all-cause mortality as compared with each of the biomarkers alone in the total patient material. XIIaA is particularly useful in predicting mortality in acute coronary syndrome patients with low troponin release, whereas BNP is effective in predicting mortality in patients with confirmed myocardial infarction and more substantial troponin release. The combination of these two biomarkers improves outcome prediction in unselected patients with chest pain and acute coronary syndrome.

Adult cystic fibrosis patients with and without infective exacerbations and their factor XII levels.

We investigated haemostatic and inflammatory parameters in patients with cystic fibrosis in an attempt to understand a previous finding of low factor XII levels in this patient population. We selected two groups of patients, adults attending outpatient annual review clinic who were well, chronically inflammed and adult patients with an infective exacerbation requiring antibiotics or admission to hospital, acutely inflammed. We measured known positive acute phase haemostatic factors, fibrinogen and factor VIII. Antithrombin and factor XII were also measured as both these factors have been proposed to be negative acute phase proteins in in-vitro cell models. Interleukin-6 was also measured as the proposed modulator of these factors during inflammation. Activated factor XII was measured to exclude XII activation as a cause of the low XII activity levels. Cystic fibrosis patients admitted to hospital with infective exacerbations, showed significantly more evidence of inflammation than the annual review patients. Fibrinogen and factor VIII were higher and factor XII was lower in these patients. This work suggests that factor XII behaves as a negative acute phase protein with no signs of elevated activated XII levels in either group. This supports similar findings from in-vitro cell culture. This study also shows low antithrombin levels in both patient populations, although there was no statistical difference between groups, which is probably related to their liver disorder.

Activated factor XII type A predicts long-term mortality in patients admitted with chest pain.

BACKGROUND: We assessed the relation between admission levels of activated factor XII type A (XIIaA), and long-term all-cause and cardiac mortality and recurrent troponin T (TnT) positive cardiovascular events in a consecutive cohort of 870 patients admitted with a clinically strongly suspected acute coronary syndrome (ACS). METHODS AND RESULTS: After a 24-month follow-up period, 138 patients (15.8%) had died and 155 (17.8%) had suffered from a recurrent TnT positive (TnT > 0.05 ng mL(-1)) event. XIIaA levels were significantly lower in long-term survivors than in patients who died (22.9 (17.7-32.1) vs. 27.2 (20.0-39.7) pmol L(-1) [median, 25 and 75% percentiles], P < 0.001). The unadjusted hazard ratio for death within 2 years in patients with XIIaA in the highest quartile was 2.49 (95% confidence interval (CI), 1.52-4.06) as compared with patients with XIIaA in the lowest quartile. In a stepwise Cox regression model for death within 2 years, XIIaA added prognostic information for all-cause mortality (HR 2.05; 95% CI, 1.21-3.47) above and beyond age, a history of heart failure, ST-segment elevation, TnT and B-type natriuretic peptide (BNP). In the subgroup of patients with an admission TnT < or = 0.05 ng mL(-1), XIIaA provided independent prognostic information for all-cause mortality (HR 3.88; 95% CI, 1.66-9.08) and for the combined endpoint of death or recurrent TnT positive event (HR 2.46; 95% CI, 1.34-4.50). CONCLUSION: XIIaA, a recently identified in vivo form of activated factor XII is an independent indicator of long-term all-cause mortality in patients admitted with chest pain, providing prognostic information above and beyond conventional risk factors.

Establishment of replacement batches for prekallikrein activator in albumin biological reference preparation.

A collaborative study was run by the European Directorate for the Quality of Medicines and HealthCare (EDQM) under the aegis of the Biological Standardisation Programme (BSP) to establish replacement batches of the current Prekallikrein activator in albumin Biological Reference Preparation (BRP) batch 1, the stocks of which were dwindling. Candidate BRP replacement batch 2 and batch 3 were assayed against the 2nd World Health Organization International Standard for Prekallikrein activator, human (2nd IS) and the Prekallikrein activator in albumin BRP batch 1. The candidate batches were manufactured from the same starting material as the current Biological Reference Preparation and the 2nd IS. They consisted of a 20 % solution of albumin lyophilised under the same conditions as the Prekallikrein activator in albumin BRP batch 1. Sixteen laboratories participated in the collaborative study and were requested to assay the candidates by their routine method, complying with the European Pharmacopoeia (Ph. Eur.) general method 2.6.15 for the determination of prekallikrein activator content. A central statistical analysis was performed at the EDQM using in-house calculations of prekallikrein activator contents provided by the participating laboratories. On the basis of the results of this study, which confirmed the assigned potency of 29 IU/vial of Prekallikrein activator in albumin BRP batch 1, the 2 candidate materials were assigned a potency of 30 IU/vial. The 2 candidates were adopted by the Ph. Eur. Commission in March 2008 as Ph. Eur. Prekallikrein activator in albumin Biological Reference Preparation batch 2 and batch 3.

Coagulation factor XII (FXII) activity, activated FXII, distribution of FXII C46T gene polymorphism and coronary risk.

BACKGROUND: Whether factor XII (FXII) activity, its 46C>T polymorphism and activated FXII (FXIIa) are associated with coronary heart disease (CHD) remains to be determined. METHODS: FXII, FXIIa and the FXII 46C>T polymorphism were determined in a hospital-based cohort of 2615 patients undergoing coronary angiography. RESULTS: Fifty-seven per cent of the participants were identified as wild-type (46CC), 38% as heterozygous (46CT) and 5% as homozygous (46TT) for FXII 46C>T. FXII and FXIIa levels were significantly lower in carriers of the T-allele: 132 (97-151) U dL(-1) FXII in 46CC, 87 (77-99) U dL(-1) FXII in 46CT and 53 (42-67) U dL(-1) FXII in 46TT carriers (P < 0.001), and 2.8 (2.3-3.5) microg L(-1) FXIIa in CC, 2.1 (1.6-2.6) microg L(-1) FXIIa in CT and 1.2 (0.9-1.5) microg L(-1) FXIIa in TT carriers (P < 0.001; medians, lower and upper quartiles). Patients with stable CHD (n = 935), a history of myocardial infarction (n = 785) or who were suffering from acute coronary syndromes (ACS; n = 323) had significantly lower FXII levels than controls (n = 572). The differences remained statistically significant after adjustments for age, sex, diabetes mellitus, smoking, hypercholesterolemia and hypertension. Significantly reduced FXIIa levels in ACS patients lost significance once adjusted for covariates. FXII genotype was not associated with any clinical phenotype. CONCLUSION: Lower FXII activity represents an independent risk for CHD and ACS. This is not the case for FXIIa levels or the FXII 46C>T variation.

Specific types of activated Factor XII increase following thrombolytic therapy with tenecteplase.

BACKGROUND: Activated Factor XII (XIIa) is believed to participate in a number of pathophysiological processes including inflammation, thrombosis and fibrinolysis. Increasing XIIa levels following thrombolytic therapy have previously been reported. In contrast to other thrombolytics, tenecteplase (TNK-tpa) does not show paradoxical thrombin activation, indicating a lower procoagulant effect of this fibrin-selective thrombolytic agent. Recent research has demonstrated that in-vivo XIIa exists in a number of different types, and the aim of this study was to investigate plasma variations of different types of XIIa following thrombolytic treatment with TNK-tpa. METHODS: Citrated blood samples were obtained from 34 patients admitted with acute ST-elevation myocardial infarction (STEMI) treated with TNK-tpa. Samples were taken immediately prior to treatment, 30-90 min after and 4 days post-treatment. XIIa measurements were performed using 2 ELISA assays designed to preferentially measure different types of XIIa; XIIaA and XIIaR. Both assays utilised a monoclonal antibody 2/215, which is highly specific for XIIa, as the solid phase capture antibody. The assay for XIIaA used a conjugate based on a polyclonal antibody against the entire XIIa molecule, whilst the assay for XIIaR incorporated a reagent to release otherwise unavailable XIIa and used a conjugate based on a monoclonal antibody against beta-XIIa. RESULTS: Changes in plasma XIIaA concentration as a result of therapy were more evident than changes in XIIaR concentration. XIIaA showed a significant increase from 67.1 (49.0-84.4) pM to 97.8 (75.5-133.1) pM [median and 25 and 75% percentiles] in the 30-90 min sample (P < 0.001), returning to pre-intervention levels 61.5 (47.5-81.0) pM by day 4. In contrast, no significant change in XIIaR concentration was observed following thrombolytic therapy with TNK-tpa. CONCLUSION: In patients admitted with STEMI, thrombolytic therapy with TNK-tpa resulted in a significant short-lasting increase in specific types of XIIa (namely XIIaA), whereas other types of XIIa (XIIaR) were largely unaffected by this intervention.