High Molecular Weight Kininogen Research Articles

Misguided by INR in Liver Disease Patients? Implications for Clinicians Including Pain Proceduralists.

THE ROSY PAST The prothrombin time (PT) assay, developed in 1935, was used in the identification of the anticoagulants dicumarol and warfarin. Currently, this assay is most commonly used to measure the therapeutic activity of warfarin. It was well known that PT results experienced a variation among centers using different reagents, making comparisons challenging. Around the same time came the invention of the international sensitivity index (ISI), allowing for calibration of different batches of thromboplastins to an international standard. To address interlaboratory PT variation, the international normalized ratio (INR), defined as the ratio of a patient’s PT to a control sample raised to the power of the ISI value, was invented in the 1980s. The INR became widely accepted after endorsement by the World Health Organization. This endorsement was only for control of oral anticoagulant therapy, as ISI calibration was specifically developed for comparing samples of patients with normal coagulation profiles to those who were anticoagulated with Coumadin (warfarin; Bristol-Myers-Squibb, New York, NY) for at least 6 weeks.1 Historically, plasma transfusions have been recommended for patients whose PT was found to be 1.5× longer than normal. Early thromboplastins in the United States had an ISI >2.0; therefore, a 1.5× increase in PT would equal an INR of 2.25. Currently, many thromboplastin reagents have an ISI close to 1.0 (World Health Organization standard); therefore, the same sample with a PT 1.5× longer than normal will equal an INR of 1.5. In the past, a PT 1.5× longer than normal indicated a moderate to severe factor deficiency (factor levels <30%), whereas today, the same value indicates only a mild factor deficiency (factor levels >40%).2 Figure 1.: The cascade model of fibrin formation. This model divides the coagulation system into separate redundant pathways (extrinsic and intrinsic) either of which can result in generation of FXa. The common pathway results in generation of thrombin and subsequent cleavage of fibrinogen to fibrin. Many of the enzymes and enzymatic complexes require Ca2+ and binding to active membrane surfaces (PL) for full activity. For simplicity, feedback activation of procofactors to cofactors and the many inhibitors of the various enzymes have been omitted. Reprinted with permission from Smith.4 Ca2+ indicates calcium; Fb, fibrin; Fg, fibrinogen; FXa, activated form of factor X; HMWK, high molecular weight kininogen; K, kallikrein; PK, prekallikrein; PL, active membrane surfaces; TF, tissue factor.

The plasma kallikrein-kininogen pathway is critical in the pathogenesis of colitis in mice

Abstract The kallikrein-kinin system (KKS) consists of two serine proteases, prekallikrein (pKal) and factor XII (FXII), and a cofactor, high-molecular-weight kininogen (HK). Although the KKS is activated in humans and animals with inflammatory bowel disease (IBD), its role in the pathogenesis of IBS has not been characterized. Here we determined the role of the KKS in the pathogenesis of IBD using mice that lack proteins involved in the KKS. In two colitis models, induced by dextran sulfate sodium (DSS) or 2,4,6-trinitrobenzene sulfonic acid (TNBS), mice deficient in HK, pKal, or bradykinin receptors displayed attenuated phenotypes including body weight loss, disease activity index, colon length shortening, reduced histological scoring, and increased colonic production of cytokines. Infiltration of neutrophils and inflammatory monocytes in the colonic lamina propria was reduced in HK-deficient mice. Reconstitution of HK-deficient mice through intravenous injection of HK recovered their susceptibility to DSS-induced colitis, increased IL-1β levels in the colon tissue, and bradykinin concentrations in plasma. In contrast to the phenotypes of other mice lacking other proteins involved in the KSS, mice lacking FXII had comparable colonic inflammation to that observed in wild-type mice. The concentration of bradykinin was significantly increased in the plasma of wild-type mice after DSS-induced colitis. In vitro DSS-induced pKal activation, HK cleavage, and bradykinin plasma release were prevented by the absence of pKal or the inhibition of Kal. Unlike DSS, TNBS-induced colitis did not trigger HK cleavage. Collectively, our data strongly suggests that Kal contributes to experimental colitis by promoting bradykinin release from HK.

ACE Inhibitor Reaction‐Induced Acute Angioedema Leading to Macroglossia: Two Case Studie

Macroglossia, either congenital or acquired enlargement of the tongue, is a rare condition that leads to functional deficiencies in speech, mastication/deglutition, and airway patency. Acute‐acquired cases of macroglossia are potentially life threatening and have myriad etiologies. Presented here are two cases of macroglossia in adults caused by acute angioedema resulting from reaction to angiotensin‐converting enzyme (ACE) inhibitors. The mechanism of ACE inhibitor‐induced angioedema is attributed to dysfunction in the kallikrien‐kinin system, a protease pathway converting high molecular weight kininogens to kinins such as bradykinin, which can lead to inflammation of the cardiovascular system. This condition, while rare in adults, is more easily diagnosed, monitored, and treated if detected early. However, many clinicians fail to educate patients on the warning signs of acute angioedema: swelling of the tongue, submandibular and pharyngeal spaces, and/or difficulty breathing. Furthermore, patients often do not recognize the symptoms of ACE inhibitor reactions, leading to delays in diagnosis and treatment. Management of acute angioedema and subsequent macroglossia includes hospitalization and intubation for airway maintenance, partial glossectomy, and subsequent glossal rehabilitation and speech therapy. Both cases presented here led to anoxic brain injury and necessitated intensive surgical intervention, demonstrating the need for better patient‐clinician communication for positive outcomes of ACE inhibitor use. Current research on the kinin system and its role in the cardiovascular system is limited, so baseline clinician‐patient education represents the best first‐line defense against life‐threatening cases of acute angioedema.Support or Funding InformationThis research is supported in part by funding from the Texas A&amp;M University College of Dentistry and the Baylor University Medical Center at Dallas.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Cell Receptor and Cofactor Interactions of the Contact Activation System and Factor XI.

The contact activation system (CAS) or contact pathway is central to the crosstalk between coagulation and inflammation and contributes to diverse disorders affecting the cardiovascular system. CAS initiation contributes to thrombosis but is not required for hemostasis and can trigger plasma coagulation via the intrinsic pathway [through factor XI (FXI)] and inflammation via bradykinin release. Activation of factor XII (FXII) is the principal starting point for the cascade of proteolytic cleavages involving FXI, prekallikrein (PK), and cofactor high molecular weight kininogen (HK) but the precise location and cell receptor interactions controlling these reactions remains unclear. FXII, PK, FXI, and HK utilize key protein domains to mediate binding interactions to cognate cell receptors and diverse ligands, which regulates protease activation. The assembly of contact factors has been demonstrated on the cell membranes of a variety of cell types and microorganisms. The cooperation between the contact factors and endothelial cells, platelets, and leukocytes contributes to pathways driving thrombosis yet the basis of these interactions and the relationship with activation of the contact factors remains undefined. This review focuses on cell receptor interactions of contact proteins and FXI to develop a cell-based model for the regulation of contact activation.

The blood fluke Schistosoma mansoni cleaves the coagulation protein high molecular weight kininogen (HK) but does not generate the vasodilator bradykinin

BackgroundSchistosomes are blood dwelling parasitic worms that cause the debilitating disease schistosomiasis. Here we examined the influence of the parasites on their external environment by monitoring the impact of adult Schistosoma mansoni worms on the murine plasma proteome in vitro and, in particular, on how the worms affect the blood coagulation protein high molecular weight kininogen (HK).MethodsFollowing the incubation of adult schistosomes in murine plasma, two-dimensional differential in-gel electrophoresis (2D-DIGE) was conducted to look for changes in the plasma proteome compared with control plasma. A major change to the blood protein kininogen (HK) was observed, and the interaction of Schistosoma mansoni parasite with this protein alone was then investigated by western blot analysis and activity assays. Finally, the generation of bradykinin from HK was monitored using a bradykinin detection kit.ResultsThe most striking change to the plasma proteome concerned HK; while the full-length protein was more abundant in control plasma, carboxyl-terminal truncated forms were more abundant in plasma that contained schistosomes. Incubating parasites in buffer with pure HK followed by Western blot analysis confirmed that human HK is degraded by the worms. The resulting digestion pattern differed from that brought about by kallikrein, a host serine protease that normally acts on HK to release the vasodilator bradykinin. We found that live schistosomes, while digesting HK, do not generate bradykinin nor do they cleave a chromogenic kallikrein substrate. Since the cleavage of HK by the worms is not impeded by the serine protease inhibitor PMSF but is blocked by the cysteine protease inhibitor E64c, we hypothesize that schistosome tegumental cysteine proteases are responsible for HK cleavage.ConclusionsSince proteomic and biochemical studies have revealed that the schistosome tegument contains two cysteine proteases belonging to the calpain family (SmCalp1 and SmCalp2) we conclude that these are likely responsible for the HK cleavage reported here. Schistosome cleavage of HK should help impede blood clotting and inflammation around the worms in vivo and so promote their ease of movement within the vasculature of their hosts.

An Extensive Study of the Functional Polymorphisms of Kinin-Kallikrein System in Rheumatoid Arthritis Susceptibility.

This study aims to examine the following functional polymorphisms in rheumatoid arthritis (RA) susceptibility: (i) the 587C>T of kininogen gene, (ii) the 287 bp Alu repeat insertion of angiotensin converting enzyme gene, (iii) the 9 bp insertion of bradykinin receptor 2 gene, (iv) the -58T>C of bradykinin receptor 2 gene, and (v) the -699G>C of bradykinin receptor 1 gene. The study included 136 RA patients (27 males; 109 females; mean age 60.8 years; range 39 to 75 years) and 149 ethnic matching controls (30 males, 119 females; mean age 56.2 years; range 35 to 78 years). Polymerase chain reaction coupled with restriction assay was performed for 587C>T, -58T>C, and -699G>C. Rheumatoid arthritis patients and controls carried the wild type allele of 587C>T; therefore, produced the high molecular weight kininogen. No significant difference was observed in genotype or allele distribution of the studied functional polymorphisms between RA patients and controls. Kinin-kallikrein system related genes might not be major RA susceptibility loci.

Interaction of the Human Contact System with Pathogens-An Update.

The name human contact system is related to its mode of action, as “contact” with artificial negatively charged surfaces triggers its activation. Today, it is generally believed that the contact system is an inflammatory response mechanism not only against artificial material but also against misfolded proteins and foreign organisms. Upon activation, the contact system is involved in at least two distinct (patho)physiologic processes:i. the trigger of the intrinsic coagulation via factor XI and ii. the cleavage of high molecular weight kininogen with release of bradykinin and antimicrobial peptides (AMPs). Bradykinin is involved in the regulation of inflammatory processes, vascular permeability, and blood pressure. Due to the release of AMPs, the contact system is regarded as a branch of the innate immune defense against microorganisms. There is an increasing list of pathogens that interact with contact factors, in addition to bacteria also fungi and viruses bind and activate the system. In spite of that, pathogens have developed their own mechanisms to activate the contact system, resulting in manipulation of this host immune response. In this up-to-date review, we summarize present research on the interaction of pathogens with the human contact system, focusing particularly on bacterial and viral mechanisms that trigger inflammation via contact system activation.

The Plasma Kallikrein-Kininogen Pathway Is Critical in the Pathogenesis of Colitis in Mice.

The kallikrein–kinin system (KKS) consists of two serine proteases, prekallikrein (pKal) and factor XII (FXII), and a cofactor, high-molecular-weight kininogen (HK). Upon activation of the KKS, HK is cleaved to release bradykinin. Although the KKS is activated in humans and animals with inflammatory bowel disease (IBD), its role in the pathogenesis of IBD has not been characterized. In the present study, we determined the role of the KKS in the pathogenesis of IBD using mice that lack proteins involved in the KKS. In two colitis models, induced by dextran sulfate sodium (DSS) or 2,4,6-trinitrobenzene sulfonic acid (TNBS), mice deficient in HK, pKal, or bradykinin receptors displayed attenuated phenotypes, including body weight loss, disease activity index, colon length shortening, histological scoring, and colonic production of cytokines. Infiltration of neutrophils and inflammatory monocytes in the colonic lamina propria was reduced in HK-deficient mice. Reconstitution of HK-deficient mice through intravenous injection of HK recovered their susceptibility to DSS-induced colitis, increased IL-1β levels in the colon tissue and bradykinin concentrations in plasma. In contrast to the phenotypes of other mice lacking other proteins involved in the KKS, mice lacking FXII had comparable colonic inflammation to that observed in wild-type mice. The concentration of bradykinin was significantly increased in the plasma of wild-type mice after DSS-induced colitis. In vitro analysis revealed that DSS-induced pKal activation, HK cleavage, and bradykinin plasma release were prevented by the absence of pKal or the inhibition of Kal. Unlike DSS, TNBS-induced colitis did not trigger HK cleavage. Collectively, our data strongly suggest that Kal, acting independently of FXII, contributes to experimental colitis by promoting bradykinin release from HK.

A novel detection method of cleaved plasma high-molecular-weight kininogen reveals its correlation with Alzheimer's pathology and cognitive impairment

IntroductionAccumulation of β-amyloid is a pathological hallmark of Alzheimer's disease (AD). β-Amyloid activates the plasma contact system leading to kallikrein-mediated cleavage of intact high-molecular-weight kininogen (HKi) to cleaved high-molecular-weight kininogen (HKc). Increased HKi cleavage is observed in plasma of AD patients and mouse models by Western blot. For potential diagnostic purposes, a more quantitative method that can measure HKc levels in plasma with high sensitivity and specificity is needed. MethodsHKi/c, HKi, and HKc monoclonal antibodies were screened from hybridomas using direct ELISA with a fluorescent substrate. ResultsWe generated monoclonal antibodies recognizing HKi or HKc specifically and developed sandwich ELISAs that can quantitatively detect HKi and HKc levels in human. These new assays show that decreased HKi and increased HKc levels in AD plasma correlate with dementia and neuritic plaque scores. DiscussionHigh levels of plasma HKc could be used as an innovative biomarker for AD.

Influence of zinc on glycosaminoglycan neutralisation during coagulation.

Heparan sulfate (HS), dermatan sulfate (DS) and heparin are glycosaminoglycans (GAGs) that serve as key natural and pharmacological anticoagulants. During normal clotting such agents require to be inactivated or neutralised. Several proteins have been reported to facilitate their neutralisation, which reside in platelet α-granules and are released following platelet activation. These include histidine-rich-glycoprotein (HRG), fibrinogen and high-molecular-weight kininogen (HMWK). Zinc ions (Zn2+) are also present in α-granules at a high concentration and participate in the propagation of coagulation by influencing the binding of neutralising proteins to GAGs. Zn2+ in many cases increases the affinity of these proteins to GAGs, and is thus an important regulator of GAG neutralisation and haemostasis. Binding of Zn2+ to HRG, HMWK and fibrinogen is mediated predominantly through coordination to histidine residues but the mechanisms by which Zn2+ increases the affinity of the proteins for GAGs are not yet completely clear. Here we will review current knowledge of how Zn2+ binds to and influences the neutralisation of GAGs and describe the importance of this process in both normal and pathogenic clotting.

Integrin-mediated leukocyte adhesive interactions: regulation by haemostatic factors.

Leukocyte recruitment to sites of inflammation, infection or vascular injury is a complex event that is orchestrated by a tightly coordinated sequence of interactions between leukocytes and cells of the vessel wall, especially endothelial cells. These interactions are controlled by the expression and activation of various adhesion receptors and protease systems. This review will focus on novel aspects of the regulation of integrin-dependent leukocyte adhesion by haemostatic factors. Here, so-called non-haemostatic properties of endogenous proteins such as high molecular weight kininogen, urokinase receptor, urokinase, as well as plasminogen and its cleavage product angiostatin in leukocyte adhesion and transmigration will be summarized. The crosstalk between haemostatic factors and inflammatory reactions may contribute to a better understanding of inflammatory vascular disorders and to the development of novel therapeutical concepts.

Streptococcus gallolyticus subsp. gallolyticus endocarditis isolate interferes with coagulation and activates the contact system

ABSTRACT Streptococcus gallolyticus subsp. gallolyticus, formerly classified as S. bovis biotype I, is an increasing cause of bacteremia and infective endocarditis in the elderly. The physiopathology of infective endocarditis is poorly understood and involves immune and coagulation systems. In this study, we found that S. gallolyticus subsp. gallolyticus activates the human contact system, which in turn has two consequences: cleavage of high-molecular-weight kininogen (HK) resulting in release of the potent pro-inflammatory peptide bradykinin, and initiation of the intrinsic pathway of coagulation. S. gallolyticus subsp. gallolyticus was found to bind and activate factors of the human contact system at its surface, leading to a significant prolongation of the intrinsic coagulation time and to the release of bradykinin. High-affinity binding of factor XII to the bacterial Pil1 collagen binding protein was demonstrated with a KD of 13 nM. Of note, Pil1 expression was exclusively found in S. gallolyticus subsp. gallolyticus, further supporting an essential contribution of this pilus in virulence.

The Search for Biomarkers in Hereditary Angioedema.

The unpredictable nature of attacks of tissue swelling in hereditary angioedema requires the identification of reliable biomarkers to monitor disease activity as well as response to therapy. At present, one can assess a C4 level (by ELISA) to assist in diagnosis but neither C4 nor C1 inhibitor levels reflect clinical course or prognosis. We will here review a collection of plasma proteins involved in blood coagulation, fibrinolysis, and innate immunity (Figure 1). A main focus is those proteins that are key to the formation of bradykinin (BK); namely, factor XII, plasma prekallikrein/kallikrein, high-molecular weight kininogen, and BK itself since overproduction of BK is key to the disease. Considerations include new approaches to measurement of active enzymes, ELISA methods that may supersede SDS gel analysis of bond cleavages, and examples of changes outside the BK cascade that may reflect when, where, and how an attack of swelling is initiated. We will discuss their usefulness as biomarker candidates, with pros and cons, and compare the analytical methods that are being developed to measure their levels or activity.

Limited role of kininogen in the host response during gram-negative pneumonia-derived sepsis.

High-molecular-weight kininogen (HK), together with factor XI, factor XII and prekallikrein, is part of the contact system that has proinflammatory, prothrombotic, and vasoactive properties. We hypothesized that HK plays a role in the host response during pneumonia-derived sepsis. To this end mice were depleted of kininogen (KNG) to plasma HK levels of 28% of normal by repeated treatment with a specific antisense oligonucleotide (KNG ASO) for 3 wk before infection with the common human sepsis pathogen Klebsiella pneumoniae via the airways. Whereas plasma HK levels increased during infection in mice treated with a scrambled control ASO (Ctrl ASO), HK level in the KNG ASO-treated group remained reduced to 25-30% of that in the corresponding Ctrl ASO group both before and after infection. KNG depletion did not influence bacterial growth in lungs or dissemination to distant body sites. KNG depletion was associated with lower lung CXC chemokine and myeloperoxidase levels but did not impact neutrophil influx, lung pathology, activation of the vascular endothelium, activation of the coagulation system, or the extent of distant organ injury. These results were corroborated by studies in mice with a genetic deficiency of KNG, which were indistinguishable from wild-type mice during Klebsiella-induced sepsis. Both KNG depletion and KNG deficiency were associated with strongly reduced plasma prekallikrein levels, indicating the carrier function of HK for this zymogen. This study suggests that KNG does not significantly contribute to the host defense during gram-negative pneumonia-derived sepsis.

Hereditary angioedema: Assessing the hypothesis for underlying autonomic dysfunction.

BackgroundAttacks of Hereditary Angioedema due to C1-inhibitor deficiency (C1-INH-HAE)are often triggered by stressful events/hormonal changes.ObjectiveOur study evaluates the relationship between autonomic nervous system (ANS) and contact/complement system activation.MethodsTwenty-three HAE patients (6 males, mean age 47.5±11.4 years) during remission and 24 healthy controls (8 males, mean age 45.3±10.6 years) were studied. ECG, beat-by-beat blood pressure, respiratory activity were continuously recorded during rest (10’) and 75-degrees-head-up tilt (10’). C1-INH, C4, cleaved high molecular weight kininogen (cHK) were assessed; in 16 patients and 11 controls plasma catecholamines were also evaluated. Spectral analysis of heart rate variability allowed extraction of low-(LF) and high-(HF) frequency components, markers of sympathetic and vagal modulation respectively.ResultsHAE patients showed higher mean systolic arterial pressure (SAP) than controls during both rest and tilt. Tilt induced a significant increase in SAP and its variability only in controls. Although sympathetic modulation (LFnu) increased significantly with tilt in both groups, LF/HF ratio, index of sympathovagal balance, increased significantly only in controls.At rest HAE patients showed higher noradrenaline values (301.4±132.9 pg/ml vs 210.5±89.6pg/ml, p = 0.05). Moreover, in patients tilt was associated with a significant increase in cHK, marker of contact system activation (49.5 ± 7.5% after T vs 47.1 ± 7.8% at R, p = 0.01).ConclusionsOur data are consistent with altered ANS modulation in HAE patients, i.e. increased sympathetic activation at rest and blunted response to orthostatic challenge. Tilt test-induced increased HK cleavage suggests a link between stress and bradykinin production.

Angiotensin-converting enzyme inhibitor-induced angioedema: A review of the literature.

According to the National Health and Nutrition Examination Survey 2012, one third of antihypertensive prescriptions in the United States in the past decade were for angiotensin-converting enzyme inhibitors (ACEIs). An important and serious side effect of ACEIs is angioedema caused by a reduction in bradykinin degradation. In a national medical chart abstraction study conducted at the US Veterans Affairs Health Care System in 2008, 0.20% of ACEI initiators developed angioedema while on the medication. The angiotensin-converting enzyme is a part of the renin-angiotensin system that converts angiotensin I to angiotensin II. It is additionally responsible for the degradation of bradykinin, which is generated from high molecular weight kininogen by kallikrein. Via bradykinin 2 receptors, bradykinin affects vascular permeability and stimulates the release of substance P, which is a peptide that causes vasodilation and fluid extravasation into tissues. Inhibition of the angiotensin-converting enzyme and subsequent blockade of bradykinin degradation is thought to be a likely explanation for ACEI-induced angioedema. Studies have shown that blacks, women, and smokers are at an increased risk for ACEI-induced angioedema. A 2005 study identified black race, history of drug rash, age older than 65years, and seasonal allergies as independent risk factors for angioedema related to enalapril. Angioedema may occur at any time during treatment with ACEIs and may continue after the medication is discontinued. The degree of ACEI-angiotensin receptor blocker angioedema cross-reactivity is difficult to determine from the literature. However, multiple studies have reported relatively low rates of native angioedema with angiotensin receptor blockers (approximately half that of ACEIs, or 0.1%) and a low incidence of cross-reactivity (<10%). Common treatments for angioedema, such as antihistamines and glucocorticoids, have not been shown to be effective in ACEI-induced angioedema. However, medications that have been used for acute treatment of hereditary angioedema and target the factors that cause ACEI-mediated angioedema are being explored.

2D-LC-MS/MS to measure cleaved high-molecular-weight kininogen in human plasma as a biomarker for C1-INH-HAE.

C1-INH-HAE is caused by activation of plasma kallikrein which subsequently cleaves high-molecular-weight kininogen (HMWK) to generate bradykinin and cHMWK. A novel ion-pair 2D LC-MS/MS assay was developed to measure the 46kDa cHMWK in plasma as a biomarker for C1-INH-HAE. The sample preparation included sodium dodecyl sulfate denaturation, methanol crash, chymotryptic digestion and peptide enrichment by solid phase extraction. The LLOQ was 200ng/ml. The overall cHMWK recovery combining crash and digestion was 57.5%. The precision of the method was ≤12.7% and accuracy ≤-13.8%. A reagent-free LC-MS assay has been developed for the quantitation of 46kDa cHMWK, which was shown to be elevated in plasma of C1-INH-HAE patients due to C1-INH deficiency relative to that of healthy subjects.

The Procoagulant Activity of Apoptotic Cells Is Mediated by Interaction with Factor XII

Apoptotic cells, by externalizing phosphatidylserine (PS) as a hallmark feature, are procoagulant. However, the mechanism by which apoptotic cells activate coagulation system remains unknown. Intrinsic coagulation pathway is initiated by coagulation factor XII (FXII) of contact activation system. The purpose of this study was to determine whether FXII is involved in procoagulant activity of apoptotic cells. Using western blotting and chromogenic substrate assay, we found that incubation with apoptotic cells, but not with viable cells, resulted in rapid cleavage and activation of FXII in the presence of prekallikrein and high molecular weight kininogen (HK), other two components of contact activation system. As detected by flow cytometry, FXII bound to apoptotic cells in a concentration-dependent manner, which was inhibited by annexin V and PS liposome. Direct association of FXII with PS was confirmed in a surface plasmon resonance assay. Clotting time of FXII-deficient plasma induced by apoptotic cells was significantly prolonged, which was fully reversed by replenishment with FXII. Corn trypsin inhibitor, a FXII inhibitor, completely prevented apoptotic cells-induced intrinsic tenase complex formation. Consistently, apoptotic cells significantly increased thrombin production in normal plasma, which was not affected by an inhibitory anti-tissue factor antibody. However, blocking of PS by annexin V, inhibition of FXII, or the deficiency of FXII suppressed apoptotic cells-induced thrombin generation. Addition of purified FXII to FXII-deficient plasma recovered thrombin generation to the normal plasma level. In conclusion, FXII binds to apoptotic cells via PS and becomes activated, thereby constituting a novel mechanism mediating the procoagulant activity of apoptotic cells.

A kallikrein‐targeting RNA aptamer inhibits the intrinsic pathway of coagulation and reduces bradykinin release

Background Plasma kallikrein is a serine protease that plays an integral role in many biological processes, including coagulation, inflammation, and fibrinolysis. The main function of kallikrein in coagulation is the amplification of activated factor XII (FXIIa) production, which ultimately leads to thrombin generation and fibrin clot formation. Kallikrein is generated by FXIIa-mediated cleavage of the zymogen prekallikrein, which is usually complexed with the non-enzymatic cofactor high molecular weight kininogen (HK). HK also serves as a substrate for kallikrein to generate the proinflammatory peptide bradykinin (BK). Interestingly, prekallikrein-deficient mice are protected from thrombotic events while retaining normal hemostatic capacity. Therefore, therapeutic targeting of kallikrein may provide a safer alternative to traditional anticoagulants with anti-inflammatory benefits. Objectives To isolate and characterize an RNA aptamer that binds to and inhibits plasma kallikrein, and to elucidate its mechanism of action. Methods and Results Using convergent Systematic Evolution of Ligands by Exponential Enrichment (SELEX), we isolated an RNA aptamer that targets kallikrein. This aptamer, Kall1-T4, specifically binds to both prekallikrein and kallikrein with similar subnanomolar binding affinities, and dose-dependently prolongs fibrin clot formation in an activated partial thromboplastin time (APTT) coagulation assay. In a purified in vitro system, Kall1-T4 inhibits the reciprocal activation of prekallikrein and FXII primarily by reducing the rate of FXIIa-mediated prekallikrein activation. Additionally, Kall1-T4 significantly reduces kallikrein-mediated HK cleavage and subsequent BK release. Conclusions We have isolated a specific and potent inhibitor of prekallikrein/kallikrein activity that serves as a powerful tool for further elucidating the role of kallikrein in thrombosis and inflammation.

An essential role of high-molecular-weight kininogen in endotoxemia.

In this study, we show that mice lacking high-molecular-weight kininogen (HK) were resistant to lipopolysaccharide (LPS)-induced mortality and had significantly reduced circulating LPS levels. Replenishment of HK-deficient mice with human HK recovered the LPS levels and rendered the mice susceptible to LPS-induced mortality. Binding of HK to LPS occurred through the O-polysaccharide/core oligosaccharide, consistent with the ability to bind LPS from K. pneumoniae, P. aeruginosa, S. minnesota, and different E. coli strains. Binding of LPS induced plasma HK cleavage to the two-chain form (HKa, containing a heavy chain [HC] and a light chain [LC]) and bradykinin. Both HKa and the LC, but not the HC, could disaggregate LPS. The light chain bound LPS with high affinity (K d = 1.52 × 10-9 M) through a binding site in domain 5 (DHG15). A monoclonal antibody against D5 significantly reduced LPS-induced mortality and circulating LPS levels in wild-type mice. Thus, HK, as a major LPS carrier in circulation, plays an essential role in endotoxemia.