Activation Of Prekallikrein Research Articles

High molecular weight kininogen interactions with the homologs prekallikrein and factor XI: importance to surface-induced coagulation

BackgroundIn plasma, high molecular weight kininogen (HK) is either free or bound to prekallikrein (PK) or factor (F) XI (FXI). During contact activation, HK is thought to anchor PK and FXI to surfaces, facilitating their conversion to the proteases plasma kallikrein and FXIa. Mice lacking HK have normal hemostasis but are resistant to injury-induced arterial thrombosis. ObjectivesTo identify amino acids on the HK-D6 domain involved in PK and FXI binding and study the importance of the HK–PK and HK–FXI interactions to coagulation. MethodsTwenty-four HK variants with alanine replacements spanning residues 542-613 were tested in PK/FXI binding and activated partial thromboplastin time clotting assays. Surface-induced FXI and PK activation in plasma were studied in the presence or absence of HK. Kng1-/- mice lacking HK were supplemented with human or murine HK and tested in an arterial thrombosis model. ResultsOverlapping binding sites for PK and FXI were identified in the HK-D6 domain. HK variants with defects only in FXI binding corrected the activated partial thromboplastin time of HK-deficient plasma poorly compared to a variant defective only in PK-binding. In plasma, HK deficiency appeared to have a greater deleterious effect on FXI activation than PK activation. Human HK corrected the defect in arterial thrombus formation in HK-deficient mice poorly due to a specific defect in binding to mouse FXI. ConclusionClinical observations indicate FXI is required for hemostasis, while HK is not. Yet, the HK–FXI interaction is required for contact activation-induced clotting in vitro and in vivo suggesting an important role in thrombosis and perhaps other FXI-related activities.

Comparative analysis of quality attributes of a human albumin preparation with a modified stabilising composition

Scientific relevance. The national and international human albumin preparations registered in the Russian Federation mainly differ in their excipient compositions. While all the international preparations of human albumin contain a mixture of sodium caprylate and N-acetyl-DL-tryptophan, the Russian ones contain only sodium caprylate. However, albumin stabilisation with sodium caprylate at high concentrations affects the ligand-binding properties of albumin. For this reason, as well as to achieve storage stability not only at temperatures of 2 °C to 8 °C but also at room temperature, most international manufacturers have reduced the sodium caprylate content in albumin preparations and added N-acetyl-DL-tryptophan. This demonstrates the relevance of studying the quality of a new Russian human albumin preparation with a modified stabilising composition, including both sodium caprylate and N-acetyl-DL-tryptophan.Aim. The study aimed at comparing several quality attributes of the human albumin preparation with a modified stabilising composition with those of imported human albumin preparations.Materials and methods. The human albumin preparation with a modified stabilising composition was manufactured by fractionation from donor plasma meeting the requirements of monograph FS.3.3.2.0001.19 of the State Pharmacopoeia of the Russian Federation edition XIV. The quality control was in line with the monograph on human albumin (FS.3.3.2.0006.18), and statistical analysis was conducted in Microsoft Excel in accordance with the general chapter on statistical analysis (OFS.1.1.0013.15).Results. The study preparation complied with the requirements specified in monograph FS.3.3.2.0006.18. All the manufactured batches were clear, thermostable, sterile, and non-pyrogenic. The prekallikrein activator levels were low (below 1 IU/mL). The aluminium content varied from 30.36±10.39 µg/L to 50.22±6.94 µg/L. The study preparation contained sodium ions at a concentration from 127.44±10.46 mmol/L to 145.59±7.32 mmol/L and less than 0.01 mmol/g of potassium ions. The osmolarity exceeded 240 mOsm/L. The content of α- and β-globulins ranged from 1.79±0.06% to 2.24±0.20%. The study preparation had a pH level of 6.9 to 7.2. The concentrations of polymers and aggregates did not exceed 0.5%.Conclusions. The quality attributes studied suggest that the human albumin preparation with a modified stabilising composition is comparable to its international counterparts and that it meets Russian and European pharmacopoeial standards.

The Properties of Extracellular Proteinase, an Activator of Blood Plasma Prekallikrein Produced by Aspergillus terreus 2 Micromycete

The Properties of Extracellular Proteinase, an Activator of Blood Plasma Prekallikrein Produced by Aspergillus terreus 2 Micromycete

C1 inhibitor and prolylcarboxypeptidase modulate prekallikrein activation on endothelial cells

We examined how prekallikrein (PK) activation on human microvascular endothelial cells (HMVECs) is regulated by the ambient concentration of C1 inhibitor (C1INH) and prolylcarboxypeptidase (PRCP). We sought to examine the specificity of PK activation on HMVECs by PRCP and the role of C1INH to regulate it, high-molecular-weight kininogen (HK) cleavage, and bradykinin (BK) liberation. Investigations were performed on cultured HMVECs. Immunofluorescence, enzymatic activity assays, immunoblots, small interfering RNA knockdowns, and cell transfections were used to perform these studies. Cultured HMVECs constitutively coexpressed PK, HK, C1INH, and PRCP. PK activation on HMVECs was modulated by the ambient C1INH concentration. In the absence of C1INH, forming PKa on HMVECs cleaved 120-kDa HK completely to a 65-kDa H-chain and a 46-kDa L-chain in 60 minutes. In the presence of 2 μM C1INH, only 50% of the HK became cleaved. C1INH concentrations (0.0-2.5 μM) decreased but did not abolish BK liberated from HK by activated PK. Factor XII did not activate when incubated with HMVECs alone for 1 hour. However, if incubated in the presence of HK and PK, factor XII became activated. The specificity of PK activation on HMVECs by PRCP was shown by several inhibitors to each enzyme. Furthermore, PRCP small interfering RNA knockdowns magnified C1INH inhibitory activity on PK activation, and PRCP transfections reduced C1INH inhibition at any given concentration. These combined studies indicated that on HMVECs, PK activation and HK cleavage to liberate BK weremodulated by the local concentrations of C1INH and PRCP.

Properties of Extracellular Proteinase – Activator of Blood Plasma Prekallikrein Produced by Micromycetes <i>Aspergillus terreus</i> 2

The extracellular proteinase – activator of human plasma prekallikrein was isolated from the culture fluid of the micromycete A. terreus 2, and their physicochemical, kinetic and biochemical properties were studied. It has been established that A. terreus 2 extracellular proteinase is a glycosylated serine proteinase with an isoelectric point of 4.6, molecular weight about 37 kDa and the optimum activity at pH 10.0 and a temperature of 37°C. In a number of properties, this proteinase is similar to proteinase – activator of protein C, which is produced by the micromycete A. ochraceus L-1.

Anti-HK antibody inhibits the plasma contact system by blocking prekallikrein and factor XI activation invivo.

A dysregulated plasma contact system is involved in various pathological conditions, such as hereditary angioedema, Alzheimer disease, and sepsis. We previously showed that the 3E8 anti-high molecular weight kininogen (anti-HK) antibody blocks HK cleavage and bradykinin generation in human plasma exvivo. Here, we show that 3E8 prevented not only HK cleavage but also factor XI (FXI) and prekallikrein (PK) activation by blocking their binding to HK in mouse plasma invivo. 3E8 also inhibited contact system-induced bradykinin generation invivo. Interestingly, FXII activation was also inhibited, likely because of the ability of 3E8 to block the positive feedback activation of FXII by kallikrein (PKa). In human plasma, 3E8 also blocked PK and FXI binding to HK and inhibited both thrombotic (FXI activation) and inflammatory pathways (PK activation and HK cleavage) of the plasma contact system activation exvivo. Moreover, 3E8 blocked PKa binding to HK and dose-dependently inhibited PKa cleavage of HK. Our results reveal a novel strategy to inhibit contact system activation invivo, which may provide an effective method to treat human diseases involving contact system dysregulation.

Preclinical Evaluation of a New Anti-COVID-19 Intravenous Immunoglobulin

Introduction. Using of immunoglobulins containing SARS-CoV-2 neutralizing antibodies may be an effective and safe tool for COVID-19 treatment. An intravenous immunoglobulin COVID-globulin from donor blood plasma containing SARS-CoV-2 neutralizing antibodies was developed at Joint-Stock Company Nacimbio.Aim. A pilot study of the safety of the "COVID-globulin".Materials and methods. When studying the safety of the preparation in animals the following parameters were evaluated: general toxicity, thrombogenic potential, influence on hematological and biochemical parameters, blood clotting and hemolytic activity, determination of local irritant action, pyrogenic properties, bacterial endotoxins, allergic effect of the drug preparation and its physicochemical characteristics.Results and discussion. Safety studies of "COVID-globulin" in animals showed no signs of intoxication, local irritant action and thrombogenic properties. Macroscopic and histological examination of the organs of rats treated with COVID-globulin showed no signs of necrosis, inflammation, atypia, or any significant pathological changes. Hematological and biochemical parameters of the blood of laboratory animals after the administration of "COVID-globulin" corresponded to the reference values. Administration of COVID-globulin to rabbits did not activate blood clot formation. The IgG subclasses distribution in the preparation corresponded to that in human plasma. The activity of the Fc-function of the immunoglobulin molecule was more than 130 % compared to the reference standard preparation, the concentration of the prekallikrein activator in the COVID-globulin ranged from 4.2 to 4.8 IU/ml, anticomplementary activity was less than 1 unit complement per 1 mg of protein.Conclusion. The results of all studies have demonstrated a high level of safety of the developed COVID-globulin preparation, which meets the safety requirements for human immunoglobulins for intravenous administration by national regulatory documents and the European Pharmacopoeia.

Human butyrylcholinesterase in Cohn fraction IV-4 purified in a single chromatography step on Hupresin.

Protection from the toxicity of nerve agents is achieved by pretreatment with human butyrylcholinesterase (BChE). Current methods for purifying large quantities of BChE from frozen Cohn fraction IV-4 produce 99% pure enzyme, but the yield is low (21%). Our goal was to simplify the purification procedure and increase the yield. Butyrylcholinesterase was extracted from frozen Cohn fraction IV-4 in 10 volumes of water pH 6. The filtered extract was pumped onto a Hupresin affinity column. The previously utilized anion exchange chromatography step was omitted. Solvent and detergent reagents used to inactivate lipid enveloped virus, bacteria and protozoa did not bind to Hupresin. BChE was eluted with 0.1 M tetramethylammonium bromide in 20 mM sodium phosphate pH 8.0. BChE protein was concentrated on a Pellicon tangential flow filtration system and demonstrated to be highly purified by mass spectrometry. A high pump rate produced protein aggregates, but a low pump rate caused minimal turbidity. Possible contamination by prekallikrein and prekallikrein activator was examined by LC-MS/MS and by a chromogenic substrate assay for kallikrein activity. Prekallikrein and kallikrein were not detected by mass spectrometry in the 99% pure BChE. The chromogenic assay indicated kallikrein activity was less than 9 mU/mL. This new, 1-step chromatography protocol on Hupresin increased the yield of butyrylcholinesterase by 200%. The new method significantly reduces production costs by optimizing yield of 99% pure butyrylcholinesterase.

Glycated albumin modulates the contact system with implications for the kallikrein-kinin and intrinsic coagulation systems

BackgroundHuman serum albumin (HSA) is the most abundant plasma protein and is sensitive to glycation in vivo. The chronic hyperglycemic conditions in patients with diabetes mellitus (DM) induce a nonenzymatic Maillard reaction that denatures plasma proteins and forms advanced glycation end products (AGEs). HSA-AGE is a prevalent misfolded protein in patients with DM and is associated with factor XII activation and downstream proinflammatory kallikrein-kinin system activity without any associated procoagulant activity of the intrinsic pathway. ObjectivesThis study aimed to determine the relevance of HSA-AGE toward diabetic pathophysiology. MethodsThe plasma obtained from patients with DM and euglycemic volunteers was probed for activation of FXII, prekallikrein (PK), and cleaved high-molecular-weight kininogen by immunoblotting. Constitutive plasma kallikrein activity was determined via chromogenic assay. Activation and kinetic modulation of FXII, PK, FXI, FIX, and FX via in vitro–generated HSA-AGE were explored using chromogenic assays, plasma-clotting assays, and an in vitro flow model using whole blood. ResultsPlasma obtained from patients with DM contained increased plasma AGEs, activated FXIIa, and resultant cleaved cleaved high-molecular-weight kininogen. Elevated constitutive plasma kallikrein enzymatic activity was identified, which positively correlated with glycated hemoglobin levels, representing the first evidence of this phenomenon. HSA-AGE, generated in vitro, triggered FXIIa-dependent PK activation but limited the intrinsic coagulation pathway activation by inhibiting FXIa and FIXa-dependent FX activation in plasma. ConclusionThese data indicate a proinflammatory role of HSA-AGEs in the pathophysiology of DM via FXII and kallikrein-kinin system activation. A procoagulant effect of FXII activation was lost through the inhibition of FXIa and FIXa-dependent FX activation by HSA-AGEs.

Titanium is a potent inducer of contact activation: implications for intravascular devices

BackgroundTitanium (Ti) and its alloys are widely used in manufacturing medical devices because of their strength and resistance to corrosion. Although Ti compounds are considered compatible with blood, they appear to support plasma contact activation and may be thrombogenic. ObjectivesThe objective of this study was to compare Ti and titanium nitride (TiN) with known activators of contact activation (kaolin and silica) in plasma-clotting assays and to assess binding and activation of factor XII, (FXII), factor XI (FXI), prekallikrein, and high-molecular-weight kininogen (HK) with Ti/TiN. MethodsTi-based nanospheres and foils were compared with kaolin, silica, and aluminum in plasma-clotting assays. Binding and activation of FXII, prekallikrein, HK, and FXI to surfaces was assessed with western blots and chromogenic assays. ResultsUsing equivalent surface amounts, Ti and TiN were comparable with kaolin and superior to silica, for inducing coagulation and FXII autoactivation. Similar to many inducers of contact activation, Ti and TiN are negatively charged; however, their effects on FXII are not neutralized by the polycation polybrene. Antibodies to FXII, prekallikrein, or FXI or coating Ti with poly-L-arginine blocked Ti-induced coagulation. An antibody to FXII reduced FXII and PK binding to Ti, kallikrein generation, and HK cleavage. ConclusionTitanium compounds induce contact activation with a potency comparable with that of kaolin. Binding of FXII with Ti shares some features with FXII binding to soluble polyanions but may have unique features. Inhibitors targeting FXII or FXI may be useful in mitigating Ti-induced contact activation in patients with titanium-based implants that are exposed to blood.

Blocking domain 6 of high molecular weight kininogen to understand intrinsic clotting mechanisms

BackgroundThe contact system is initiated by factor (F) XII activation and the assembly of high molecular weight kininogen (HK) with either FXI or prekallikrein (PK) on a negatively charged surface. Overactivation ofsystem contributes to thrombosis and inflammation in numerous diseases. To develop effective therapeutics for contact system disorders, a detailed understanding ofpathway is needed. MethodsWe performed coagulation assays in normal human plasma and various factor‐deficient plasmas. To evaluate how HK‐mediated PK and FXI activation contributes to coagulation, we used an anti‐HK antibody to block access to domain 6 of HK, the region required for efficient activation of PK and FXI. ResultsFXI's binding to HK and its subsequent activation by activated FXII contributes to coagulation. We found that the 3E8 anti‐HK antibody can inhibit the binding of FXI or PK to HK, delaying clot formation in human plasma. Our data show that in the absence of FXI, however, PK can substitute for FXI inprocess. Addition of activated FXI (FXIa) or activated PK (PKa) abolished the inhibitory effect of 3E8. Moreover, the requirement of HK in intrinsic coagulation can be largely bypassed by adding FXIa. Like FXIa, exogenous PKa shortened the clotting time in HK‐deficient plasma, which was not due to feedback activation of FXII. Conclusionsstudy improves our understanding of HK‐mediated coagulation and provides an explanation for the absence of bleeding in HK‐deficient individuals. 3E8 specifically prevented HK‐mediated FXI activation; therefore, it could be used to prevent contact activation‐mediated thrombosis without altering hemostasis.

Recent advances in factor XII structure and function.

Factor XII (FXII), the precursor of the protease FXIIa, contributes to pathologic processes including angioedema and thrombosis. Here, we review recent work on structure-function relationships for FXII based on studies using recombinant FXII variants. FXII is a homolog of pro-hepatocyte growth factor activator (Pro-HGFA). We prepared FXII in which domains are replaced by corresponding parts of Pro-HGA, and tested them in FXII activation and activity assays. In solution, FXII and prekallikrein undergo reciprocal activation to FXIIa and kallikrein. The rate of this process is restricted by the FXII fibronectin type-2 and kringle domains. Pro-HGA replacements for these domains accelerate FXII and prekallikrein activation. When FXII and prekallikrein bind to negatively charged surfaces, reciprocal activation is enhanced. The FXII EGF1 domain is required for surface binding. We propose a model in which FXII is normally maintained in a closed conformation resistant to activation by intramolecular interactions involving the fibronectin type-2 and kringle domains. These interactions are disrupted when FXII binds to a surface through EGF1, enhancing FXII activation and prekallikrein activation by FXIIa. These observations have important implications for understanding the contributions of FXII to disease, and for developing therapies to treat thrombo-inflammatory disorders.

Identification of the histidine‐rich glycoprotein domains responsible for contact pathway inhibition

BackgroundPreviously, we showed that histidine‐rich glycoprotein (HRG) binds factor (F) XIIa with high affinity, inhibits FXII autoactivation and FXIIa‐mediated activation of FXI, and attenuates ferric chloride‐induced arterial thrombosis in mice. Therefore, HRG downregulates the contact pathway in vitro and in vivo. ObjectiveTo identify the domains on HRG responsible for contact pathway inhibition. MethodsRecombinant HRG domain constructs (N‐terminal [N1, N2, and N1N2], proline‐rich regions, histidine‐rich region [HRR], and C‐terminal) were expressed and purified. The affinities of plasma‐derived HRG, HRG domain constructs, and synthetic HRR peptides for FXII, FXIIa, β‐FXIIa, and polyphosphate (polyP) were determined using surface plasmon resonance, and their effects on polyP‐induced FXII autoactivation, FXIIa‐mediated activation of FXI and prekallikrein, the activated partial thromboplastin time (APTT), and thrombin generation were examined. ResultsHRG and HRG domain constructs bind FXIIa, but not FXII or β‐FXII. HRR, N1, and N1N2 bind FXIIa with affinities comparable with that of HRG, whereas the remaining domains bind with lower affinity. Synthetic HRR peptides bind FXIIa and polyP with high affinity. HRG and HRR significantly inhibit FXII autoactivation and prolong the APTT. Like HRG, synthetic HRR peptides inhibit FXII autoactivation, attenuate FXIIa‐mediated activation of prekallikrein and FXI, prolong the APTT, and attenuate thrombin generation. ConclusionThe interaction of HRG with FXIIa and polyP is predominantly mediated by the HRR domain. Like intact HRG, HRR downregulates the contact pathway and contributes to HRG‐mediated down regulation of coagulation.

Standardisation of the method for prekallikrein activator determination in human immunoglobulin and albumin products

Assessment of prekallikrein content is essential for safety control of human immunoglobulin and albumin products. The inherent variability of human prekallikrein reagents and chromogenic substrates indicates the need for standardisation of the chromogenic assay, using the components of a reference standard (RS) not only for construction of calibration curves, but also for confirmation of validity, consistency, and reproducibility of results within different established ranges. The aim of the study was to improve the quality control of human plasma products in terms of prekallikrein activator content. Materials and methods: prekallikrein activator content was determined by the chromogenic assay according to the procedure described in General Monograph 1.8.2.0013.18 of the Russian Pharmacopoeia, using various prekallikrein reagents. An RS was developed in a spiking test, using human albumin solution and Hageman factor beta-fragment reagent. Shewhart control charts were prepared based on the results of determination of prekallikrein activator content in the RS control component.Results: a two-component RS for prekallikrein activator content with an assigned Hageman factor beta fragment content was developed using the spiking test. The authors substantiated the necessity of using a Russian-produced prekallikrein reagent as the RS component. The in-house reference standard IRS 42-28-445 was certified using all available human prekallikrein reagents, and the IRS 42-28-446 was certified using the prekallikrein reagent included in the kit. The certified prekallikrein activator content is: 51 IU in the batches 1 of IRS components intended for prekallikrein determination; 8.3–11.9 IU/mL in the IRS 42-28-445 control component, after reconstitution in 1.0 mL of purified water, and 5.4–6.6 IU/mL after reconstitution in 2.0 mL of purified water; and 9.1–11.1 IU/mL and 5.6–6.4 IU/mL in the IRS 42-28-446 control component after reconstitution in 1.0 mL and 2.0 mL of purified water, respectively. The IRS component intended for prekallikrein determination is designed for calibration curve construction, while the IRS control component is designed for assessing the validity of test results and preparation of control charts. The analysis of the control charts for the control component made it possible to evaluate the consistency of the analytical process. Conclusions: the components of the developed RSs in combination with Shewhart control charts allow for both determination of prekallikrein activator content, and control of the analytical process, as well as assessment of changes related to the replacement of the reagent batch. The RS control component allows for assessment of analytical process consistency and ensures the standardisation of the test procedure.

Model for surface-dependent factor XII activation: the roles of factor XII heavy chain domains

AbstractFactor XII (FXII) is the zymogen of a plasma protease (FXIIa) that contributes to bradykinin generation by converting prekallikrein to the protease plasma kallikrein (PKa). FXII conversion to FXIIa by autocatalysis or PKa-mediated cleavage is enhanced when the protein binds to negatively charged surfaces such as polymeric orthophosphate. FXII is composed of noncatalytic (heavy chain) and catalytic (light chain) regions. The heavy chain promotes FXII surface-binding and surface-dependent activation but restricts activation when FXII is not surface bound. From the N terminus, the heavy chain contains fibronectin type 2 (FN2), epidermal growth factor-1 (EGF1), fibronectin type 1 (FN1), EGF2, and kringle (KNG) domains and a proline-rich region. It shares this organization with its homolog, pro–hepatocyte growth factor activator (Pro-HGFA). To study the importance of heavy chain domains in FXII function, we prepared FXII with replacements of each domain with corresponding Pro-HGFA domains and tested them in activation and activity assays. EGF1 is required for surface-dependent FXII autoactivation and surface-dependent prekallikrein activation by FXIIa. KNG and FN2 are important for limiting FXII activation in the absence of a surface by a process that may require interactions between a lysine/arginine binding site on KNG and basic residues elsewhere on FXII. This interaction is disrupted by the lysine analog ε-aminocaproic acid. A model is proposed in which an ε-aminocaproic acid–sensitive interaction between the KNG and FN2 domains maintains FXII in a conformation that restricts activation. Upon binding to a surface through EGF1, the KNG/FN2-dependent mechanism is inactivated, exposing the FXII activation cleavage site.

Contact system activation in disseminated intravascular coagulation: activities of prekallikrein and high-molecular-weight kininogen are significant risk factors.

The contact system activation can play a role in microthrombus formation of disseminated intravascular coagulation (DIC). This study investigated whether the activity of prekallikrein and high-molecular-weight kininogen (HMWK) correlated DIC progression. Contact system factors (prekallikrein, HMWK, activated factor XII), coagulation factors (IX, XI, XII) and tissue factor were measured in 140 patients who clinically suspected of having DIC. Prekallikrein and HMWK activity levels showed significant linear relationships with DIC score and antithrombin level, whereas prekallikrein and HMWK antigen levels did not. The activated factor XII, factor XII, factor XI and tissue factor were significant risk factors of overt-DIC. This finding suggests that consumption of prekallikrein and HMWK contributes to microvascular thrombosis in DIC. Measurements of prekallikrein and HMWK activity could be used as potential diagnostic markers for overt-DIC.

Factor VII activating protease (FSAP) is not essential in the pathophysiology of angioedema in patients with C1 inhibitor deficiency

BackgroundExcessive bradykinin (BK) generation from high molecular weight kininogen (HK) by plasma kallikrein (PK) due to lack of protease inhibition is central to the pathophysiology of hereditary angioedema (HAE). Inadequate protease inhibition may contribute to HAE through a number of plasma proteases including factor VII activating protease (FSAP) that can also cleave HK. ObjectiveTo investigate the interaction between FSAP and C1 inhibitor (C1Inh) and evaluate the potential role of FSAP in HAE with C1Inh deficiency. Materials and methodsPlasma samples from 20 persons with HAE types 1 or 2 in remission were studied and compared to healthy controls. We measured and compared antigenic FSAP levels, spontaneous FSAP activity, FSAP generation potential, activation of plasma pre-kallikrein (PPK) by FSAP, and the formation of FSAP-C1Inh and FSAP-alpha2-antiplasmin (FSAP-α2AP) complexes. Furthermore, we measured HK cleavage and PK activation after activation of endogenous pro-FSAP and after addition of exogenous FSAP. ResultsIn plasma from HAE patients, there is increased basal FSAP activity compared to healthy volunteers. HAE plasma exhibits decreased formation of FSAP-C1Inh complexes and increased formation of FSAP-α2AP complexes in histone-activated plasma. Although exogenous FSAP can cleave HK in plasma, this was not seen when endogenous plasma pro-FSAP was activated with histones in either group. PK was also not activated by FSAP in plasma. ConclusionIn this study, we established that FSAP activity is increased and the pattern of FSAP-inhibitor complexes is altered in HAE patients. However, we did not find evidence suggesting that FSAP contributes directly to HAE attacks.

Comparison of Contaminant Profiles and Biochemical Properties for Commercial Preparations of Immune Globulin Intravenous (IGIV)

Immune globulin intravenous (IGIV) has grown steadily in the volume of use and numbers of clinical indications since the first modern commercial preparation was approved by FDA in 1981. All US-marketed IGIV products are approved by FDA to treat primary immune deficiency; seven are also approved for immune thrombocytopenia purpura. Currently, most IGIV infusions are for treating autoimmune diseases.IGIV has historically been isolated from pools of human plasma (at least 1,000 donors, but typically ranging from 10,000 donations in the US up to 60,000 donations in some EU nations) using Cohn-Oncley cold ethanol fractionation. Most firms now supplement this process with chromatographic steps to remove Factor XIa, other promoters of complement activation, and other Ig isotypes.Despite high purity, a range of adverse symptoms, varying widely by product, is associated with IGIV infusions. To date, a possible correlation between adverse event profiles and contaminant profiles for IGIV products has not been studied and remains poorly understood. FDA requires donor blood tests for absence of hepatitis, HIV and other viral diseases. Final container immunoglobulin products must show potency against measles, diphtheria and polio virus and contain no prekallikrein activator. However, no further characterization of contaminant proteins is currently required.We therefore undertook comparative component analyses of 5% and 10% solution IGIV products approved or in development for the US market. Component analysis was performed using high resolution mass spectrometry (HRMS) and very sensitive multiplexed ELISA (mELISA) surveys to identify and quantitate trace contaminants in individual products. Factor XIa antigen and activity tests as well as functional assays were performed to assess the thrombogenic potential of the products. Subgroup and Ig isotype distribution were assessed by ELISA, and size exclusion chromatography was used to determine the extent of molecular aggregation.HRMS and mELISA are complementary but fundamentally different survey methods. HRMS is less “biased” in that it will detect any molecular entity more abundant than the limit of detection, whereas mELISA detected primarily biomarkers included in lists of assays preset by the vendor. Among these were several tumor markers, a wide range of inflammatory modulators, and a number of metabolic hormones.For a complex biologic such as polyclonal IGIV, HRMS typically detects entities present at levels of 10 - 20 molar ppm, while the lower limit of quantitation (LLOQ) of the mELISA is typically 3 - 5 orders of magnitude lower. Therefore, the mELISA survey of each IGIV product typically detects a substantially greater number of contaminant entities than the HRMS assay. If mELISA found a protein at ≥ 10 ppm for a product, it was generally also among the contaminants detected by HRMS. Thus, HRMS and mELISA results correlated satisfactorily. With both methods, detected levels of any given contaminant varied up to several orders of magnitude among the IGIV products tested.The most abundant contaminants in most preparations were IgA, IgD, β 2-glycoprotein-1, α 2-macroglobulin and albumin. Residual albumin and IgM were found in some but not all products. Inflammatory modulators were largely absent from the IGIV products surveyed. The interleukins IL6, IL-8 and IL-10 were detected in a few products, but in no case more than 4-fold above the mELISA LLOQ. The tumor markers carcinoembryonic antigen (CEA), α-fetoprotein (αFP), CA-125, CA 19-9 and tumor necrosis factor-α were not found in any product.The results of these assays are discussed with respect to their potential relationship to the observed adverse event and safety profiles of the individual products. DisclosuresAbramson: GC Mogam, Incorporated: Consultancy, Research Funding. Van Cott: GC Mogam, Incorporated: Research Funding.

Severe High Molecular Weight Kininogen (HK) Deficiency: Clinical Characteristics, Deficiency-Causing KNG1 Variants in Reported and New Cases, and Estimated Prevalence

Background: Severe high molecular weight kininogen (HK) deficiency is an autosomal recessive defect of the contact system caused by mutations in KNG1. Limited scientific interest in HK deficiency due to the rarity of the seemingly asymptomatic condition may increase, as HK, the precursor of bradykinin, is now discussed as a therapeutic target e.g. in hereditary angioedema.Aims: We provide a comprehensive analysis of the diagnostic, clinical, and genetic features of HK deficiency and estimate its frequency.Methods: We identified a new case of HK deficiency, systematically review the literature, conduct new genetic studies of reported cases, and comprehensively analyze the clinical course and diagnostic criteria. Clotting activity of HK and prekallikrein (PK) (HK:C/PK:C) and antigen (HK:Ag/PK:Ag) were determined and genetic analyses of KNG1 and KLKB1 were performed by Sanger sequencing. Characteristics deduced from the known HK deficiency-causing variants were used to estimate the frequency of HK deficiency from the KNG1 variants aggregated in GnomAD.Results: 677 studies were identified by systematic review of the literature for HK deficiency. 27 of these contained individual cases of HK deficiency including 6 studies not listed in PubMed. Little-noticed cases from the gray literature account for more than one-third (16/39) of the extracted, unrelated cases. We genotyped one newly diagnosed HK-deficient case and 2 cases described in the literature and additionally evaluated all 10 studies reporting genetic data in HK-deficiency (including one case previously misdiagnosed as having PK deficiency). A total of 10 KNG1 variants causing HK deficiency (one new) were found, the most frequent being c.586C>T, p.Arg196* (4 unrelated families). Interestingly, all HK deficiency-causing variants are truncating, whereas two amino acid substitutions with presumed functional consequence, have been described as the cause of hereditary angioedema. Conservative prevalence estimates based on all known and putative HK deficiency-causing variants extracted from GnomAD (truncating variants in KNG1, including indels, nonsense and canonical splice site mutations located in that part of the gene, where relevant mutations have been described) revealed a frequency of 1 case of HK deficiency among 7,925,172 with slight differences in the analyzed ethnicities (see table). In addition, although not to the same extent as seen in PK deficiency, HK deficiency apparently is more prevalent in Africans.While it is already well known that HK deficiency causes decreased PK levels, our data indicate that factor XI levels are also frequently decreased, albeit to a lesser extent.The number of cases detected so far is too low for a more detailed analysis regarding bleeding, thrombotic, and cardiovascular events or immunological abnormalities.Conclusion: HK-deficiency is probably more frequent than previously thought. Suspected cases of contact phase defects should at least be analyzed for HK activity (besides factor XII, XI and PK activity) to facilitate conclusive evaluation of the clinical significance in the future. [Display omitted] DisclosuresLämmle: Takeda: Membership on an entity's Board of Directors or advisory committees; Ablynx: Membership on an entity's Board of Directors or advisory committees, Other: Travel Support, Speakers Bureau; Baxter: Other: Travel Support, Speakers Bureau; Alexion: Other: Travel Support, Speakers Bureau; Siemens: Other: Travel Support, Speakers Bureau; Bayer: Other: Travel Support, Speakers Bureau; Roche: Other: Travel Support, Speakers Bureau; Sanofi: Other: Travel Support, Speakers Bureau.

Predictive Value for Increased Factor XIa and Plasma Kallikrein Activity in Acute Venous Thromboembolism

Venous thromboembolism (VTE) is associated with increased coagulation activity, which in part can be attributed to the contact pathway of coagulation. Evidence from pre-clinical and epidemiological studies suggests that deficiency in factors of contact activation (e.g. coagulation factors (F) XI and FXII) protects against VTE. However, limited information exists regarding the activation of the contact system in the setting of acute VTE.In the current study, patients with confirmed VTE events (n=321) from the VTEval study and controls (n=300) from the population-based PREVENT-it pilot study were included. Plasma samples were collected from patients after confirmed VTE events or controls upon inclusion in the study. FXI as well as FXIa and plasma kallikrein (PKa) levels were assessed in plasma samples from all subjects using an activated thromboplastin time-based assay (FXI:c), a thrombin generation-based assay (CAT:FXIa) and by measuring inhibitory complexes (FXIa:antithrombin (AT), FXIa:alpha-1-antitrypsin (α1AT), FXIa:C1 esterase inhibitor (C1Inh) and PKa:C1Inh) using enzyme-linked immunoassay (ELISA). After a 2-year follow up period, a composite endpoint of recurrent VTE or death was determined.Increased FXI:c levels were determined in VTE patients compared to control individuals (124.08 ± 37.48% vs. 113.55 ± 27.99%), whereas CAT:FXIa levels were reduced in VTE patients (0 pM [IQR, 0-0.56] vs 0.56 pM [IQR, 0-0.88]). Levels of FXIa:α1AT and FXIa:AT inhibitory complexes were increased in VTE patients compared to controls (median[IQR]; 311.8 pM [238.2-424.0] vs. 202.5 pM [143.7 - 287.5] and 29.1 pM [23.4-38.3] vs 23.2 pM [19.7-29.8], respectively). Considering that 86% of the VTE patients were already on anticoagulant treatment (Table 1), investigation of their possible effect on the biomarkers revealed that only the CAT:FXIa was influenced by the presence of anticoagulants. Logistic regression models revealed a good discriminatory value for FXI:c and FXIa:α1AT (AUC=0.64 [0.6/0.69] and AUC=0.67 [0.62/0.71], respectively) to distinguish VTE from controls, whereas the other biomarkers were not able to distinguish between groups. The outcome recurrent VTE or death could be predicted by the inhibitory complexes, but not by the FXI(a) levels (Figure 1). Only the FXIa:α1AT complexes were able to both detect the presence of VTE (OR per SD [95%CI]: 1.28 [1.01-1.63], p=0.04) and predict recurrent VTE or death (HR per SD [95%CI]: 1.40 [1.2-1.62], p<0.0001).In summary, acute VTE is associated with both elevated FXI:c levels and increased activation of FXI and plasma prekallikrein, the latter specifically indicating contact activation. The generation of FXIa during acute VTE and its association with recurrent VTE suggests an important risk contribution of FXI activation. This study has added evidence favouring the utility of FXIa inhibition in the setting of acute VTE. [Display omitted] DisclosuresKnoeck: Bayer AG: Consultancy. ten Cate: Bayer AG: Other; Pfizer: Other; LEO Pharma: Other; Gideon Pharmaceuticals: Other; Alveron Pharma: Other. Wild: Bayer AG: Other, Research Funding; Boehringer Ingelheim: Other, Research Funding; Novartis Pharma: Other, Research Funding; Sanofi-Aventis: Other, Research Funding; Astra Zeneca: Other, Research Funding; Daiichi Sankyo Europe: Other, Research Funding.