Assembly, activation, and physiologic influence of the plasma kallikrein/kinin system

A Rare Cause of Isolated Prolonged Activated Partial Thromboplastin Time: An Overview of Prekallikrein Deficiency and the Contact System

Prekallikrein (PK) deficiency, also known as Fletcher factor deficiency, is a very rare disorder inherited as an autosomal recessive trait. It is usually identified incidentally in asymptomatic patients with a prolonged activated partial thromboplastin time (aPTT). In this article, we present the case of a 52-year-old woman, with no prior personal or family history of thrombotic or hemorrhagic disorders, who was noted to have substantial protracted aPTT through the routine coagulation assessment before a kidney biopsy. The patient had an uneventful biopsy course after receiving fresh frozen plasma (FFP). Laboratory investigations performed before the biopsy indicated normal activity for factors VIII, IX, XI, XII, and von Willebrand factor (vWF) as well as negative lupus anticoagulant (LA) screen. The plasma PK assay revealed low activity at 15% consistent with mild PK deficiency. The deficit of PK is characterized by a severely prolonged aPTT and normal prothrombin time (PT) in the absence of bleeding tendency. PK plays a role in the contact-activated coagulation pathway and the inflammatory response. Thus, other differential diagnoses of isolated prolonged aPTT include intrinsic pathway factor deficiencies and nonspecific inhibitors such as LA. We concluded that the initial evaluation of a prolonged aPTT with normal PT should appraise the measurement of contact activation factors and factor inhibitors. PK deficiency should be considered in asymptomatic patients with isolated aPTT prolongation, which corrects on incubation, with normal levels of the contact activation factors and factor inhibitors.

Novel anti-thrombotic mechanisms mediated by Mas receptor as result of balanced activities between the kallikrein/kinin and the renin-angiotensin systems

The risk of thrombosis, a globally growing challenge and a major cause of death, is influenced by various factors in the intravascular coagulation, vessel wall, and cellular systems. Among the contributors to thrombosis, the contact activation system and the kallikrein/kinin system, two overlapping plasma proteolytic systems that are often considered as synonymous, regulate thrombosis from different aspects. On one hand, components of the contact activation system such as factor XII initiates activation of the coagulation proteins promoting thrombus formation on artificial surfaces through factor XI- and possibly prekallikrein-mediated intrinsic coagulation. On the other hand, physiological activation of plasma prekallikrein in the kallikrein/kinin system on endothelial cells liberates bradykinin from associated high-molecular-weight kininogen to stimulate the constitutive bradykinin B2 receptor to generate nitric oxide and prostacyclin to induce vasodilation and counterbalance angiotensin II signaling from the renin-angiotensin system which stimulates vasoconstriction. In addition to vascular tone regulation, this interaction between the kallikrein/kinin and renin-angiotensin systems has a thrombo-regulatory role independent of the contact pathway. At the level of the G-protein coupled receptors of these systems, defective bradykinin signaling due to attenuated bradykinin formation and/or decreased B2 receptor expression, as seen in murine prekallikrein and B2 receptor null mice, respectively, leads to compensatory overexpressed Mas, the receptor for angiotensin-(1-7) of the renin-angiotensin system. Mas stimulation and/or its increased expression contributes to maintaining a healthy vascular homeostasis by generating graded elevation of plasma prostacyclin which reduces thrombosis through two independent pathways: (1) increasing the vasoprotective transcription factor Sirtuin 1 to suppress tissue factor expression, and (2) inhibiting platelet activation. This review will summarize the recent advances in this field that support these understandings. Appreciating these subtle mechanisms help to develop novel anti-thrombotic strategies by targeting the vascular receptors in the renin-angiotensin and the kallikrein/kinin systems to maintain healthy vascular homeostasis.

Kininogen supports inflammation and bacterial spreading during Streptococccus Pyogenes Sepsis

BACKGROUND

High-molecular-weight kininogen is a cofactor of the human contact system, an inflammatory response mechanism that is activated during sepsis. It has been shown that high-molecular-weight kininogen contributes to endotoxemia, but is not critical for local host defense during pneumonia by Gram-negative bacteria. However, some important pathogens, such as Streptococcus pyogenes, can cleave kininogen by contact system activation. Whether kininogen causally affects antibacterial host defense in S. pyogenes infection, remains unknown.

METHODS

Kininogen concentration was determined in course plasma samples from septic patients. mRNA expression and degradation of kininogen was determined in liver or plasma of septic mice. Kininogen was depleted in mice by treatment with selective kininogen directed antisense oligonucleotides (ASOs) or a scrambled control ASO for 3 weeks prior to infection. 24 h after infection, infection parameters were determined.

FINDINGS

Data from human and mice samples indicate that kininogen is a positive acute phase protein. Lower kininogen concentration in plasma correlate with a higher APACHE II score in septic patients. We show that ASO-mediated depletion of kininogen in mice indeed restrains streptococcal spreading, reduces levels of proinflammatory cytokines such as IL-1β and IFNγ, but increased intravascular tissue factor and fibrin deposition in kidneys of septic animals.

INTERPRETATION

Mechanistically, kininogen depletion results in reduced plasma kallikrein levels and, during sepsis, in increased intravascular tissue factor that may reinforce immunothrombosis, and thus reduce streptococcal spreading. These novel findings point to an anticoagulant and profibrinolytic role of kininogens during streptococcal sepsis.

FUNDING

Full details are provided in the Acknowledgements section.

Intrinsic Coagulation Pathway, History of Headache, and Risk of Ischemic Stroke

Background and Purpose—

Hypercoagulable states in migraine patients may play a role in the pathophysiology underlying the association between migraine and ischemic stroke. This study aims to provide more insight into the potential association of headache, ischemic stroke, and the intrinsic coagulation pathway.

Methods—

We included patients from the RATIO study (Risk of Arterial Thrombosis in Relation to Oral Contraceptives), a Dutch population-based case-control study including young women (age <50) with ischemic stroke and healthy controls. We defined a headache group based on a questionnaire on headache history. Intrinsic coagulation proteins were measured through both antigen levels (FXII, FXI, prekallikrein, HK [high molecular weight kininogen]) and protein activation, determined by measuring activated protein complex with C1esterase-inhibitor (FXIIa-C1-INH, FXIa-C1-INH, Kallikrein-C1-INH) or antitrypsin-inhibitor (FXIa-AT-INH). We calculated adjusted odds ratios and performed an interaction analysis assessing the increase in stroke risk associated with high levels of intrinsic coagulation and history of headache.

Results—

We included 113 ischemic stroke cases and 598 healthy controls. In total, 134 (19%) patients had a history of headache, of whom 38 were cases and 96 controls. The combination of headache and high intrinsic coagulation protein levels (all but FXII antigen level and both FXIa-inhibitors) was associated with an increase in ischemic stroke risk higher than was expected based on their individual effects (adjusted odds ratio FXI antigen level alone: 1.7, 95% CI, 1.0–2.9; adjusted odds ratio headache alone: 2.0, 95% CI, 1.1−3.7; combination: 5.2, 95% CI, 2.3−11.6)

Conclusions—

Headache and high intrinsic coagulation protein levels may biologically interact, increasing risk for ischemic stroke.

Plasma kallikrein modulates immune cell trafficking during neuroinflammation via PAR2 and bradykinin release

Blood-brain barrier (BBB) disruption and transendothelial trafficking of immune cells into the central nervous system (CNS) are pathophysiological hallmarks of neuroinflammatory disorders like multiple sclerosis (MS). Recent evidence suggests that the kallikrein-kinin and coagulation system might participate in this process. Here, we identify plasma kallikrein (KK) as a specific direct modulator of BBB integrity. Levels of plasma prekallikrein (PK), the precursor of KK, were markedly enhanced in active CNS lesions of MS patients. Deficiency or pharmacologic blockade of PK renders mice less susceptible to experimental autoimmune encephalomyelitis (a model of MS) and is accompanied by a remarkable reduction of BBB disruption and CNS inflammation. In vitro analysis revealed that KK modulates endothelial cell function in a protease-activated receptor-2-dependent manner, leading to an up-regulation of the cellular adhesion molecules Intercellular Adhesion Molecule 1 and Vascular Cell Adhesion Molecule 1, thereby amplifying leukocyte trafficking. Our study demonstrates that PK is an important direct regulator of BBB integrity as a result of its protease function. Therefore, KK inhibition can decrease BBB damage and cell invasion during neuroinflammation and may offer a strategy for the treatment of MS.

Impact of Bradykinin Generation During Thrombolysis in Ischemic Stroke

Ischemic stroke is one of the leading causes of death and disability worldwide. Current medical management in the acute phase is based on the activation of the fibrinolytic cascade by intravenous injection of a plasminogen activator (such as tissue-type plasminogen activator, tPA) that promotes restauration of the cerebral blood flow and improves stroke outcome. Unfortunately, the use of tPA is associated with deleterious effects such as hemorrhagic transformation, symptomatic brain edema, and angioedema, which limit the efficacy of this therapeutic strategy. Preclinical and clinical evidence suggests that intravenous thrombolysis generates large amounts of bradykinin, a peptide with potent pro-inflammatory, and pro-edematous effects. This tPA-triggered generation of bradykinin could participate in the deleterious effects of thrombolysis and is a potential target to improve neurological outcome in tPA-treated patients. The present review aims at summarizing current evidence linking thrombolysis, bradykinin generation, and neurovascular damage.

Improving the understanding of plasma kallikrein contribution to arterial thrombus formation using two plant protease inhibitors

The purpose of antithrombotic therapy is the prevention of thrombus formation and/or its extension with a minimum risk of bleeding. The inhibition of a variety of proteolytic processes, particularly those of the coagulation cascade, has been reported as a property of plant protease inhibitors. The role of trypsin inhibitors (TIs) from Delonix regia (Dr) and Acacia schweinfurthii (As), members of the Kunitz family of protease inhibitors, was investigated on blood coagulation, platelet aggregation, and thrombus formation. Different from Acacia schweinfurthii trypsin inhibitor (AsTI), Delonix regia trypsin inhibitor (DrTI) is a potent inhibitor of FXIa with a K_iapp of 1.3 × 10^-9 M. In vitro, both inhibitors at 100 µg corresponding to the concentrations of 21 μM and 15.4 μM of DrTI and AsTI, respectively, increased approximately 2.0 times the activated partial thromboplastin time (aPTT) in human plasma compared to the control, likely due to the inhibition of human plasma kallikrein (huPK) or activated factor XI (FXIa), in the case of DrTI. Investigating in vivo models of arterial thrombus formation and bleeding time, DrTI and AsTI, 1.3 µM and 0.96 µM, respectively, prolonged approximately 50% the time for total carotid artery occlusion in mice compared to the control. In contrast to heparin, the bleeding time in mice treated with the two inhibitors did not differ from that of the control group. DrTI and AsTI inhibited 49.3% and 63.8%, respectively, ex vivo murine platelet aggregation induced by adenosine diphosphate (ADP), indicating that these protein inhibitors prevent arterial thrombus formation possibly by interfering with the plasma kallikrein (PK) proteolytic action on the intrinsic coagulation pathway and its ability to enhance the platelet aggregation activity on the intravascular compartment leading to the improvement of a thrombus.

Factor VII activating protease

Factor VII activating protease (FSAP) is a circulating serine protease with high homology to fibrinolytic enzymes. A role in the regulation of coagulation and fibrinolysis is suspected based on in vitro studies demonstrating activation of FVII or pro-urokinase plasminogen activator (uPA). However, considering the paucity of any studies in animal models or any correlative studies in humans the role of FSAP in haemostasis remains unclear. In relation to vascular remodeling processes or inflammation it has been convincingly shown that FSAP interacts with growth factors as well as protease activated receptors (PAR). Against this sparse background there are a plethora of studies which have investigated the linkage of single nucleotide polymorphisms (SNP) in the FSAP gene (HABP2) to various diseases. The G534E SNP of FSAP is associated with a low proteolytic activity due to an amino acid exchange in the protease domain. This and other SNPs have been linked to carotid stenosis, stroke as well as thrombosis in the elderly and plaque calcification. These SNP analyses indicate an important role for FSAP in the regulation of the haemostasis system as well as fibroproliferative inflammatory processes.

Zinc: An important cofactor in haemostasis and thrombosis

There is mounting evidence that zinc, the second most abundant transition metal in blood, is an important mediator of haemostasis and thrombosis. Prompted by the observation that zinc deficiency is associated with bleeding and clotting abnormalities, there now is evidence that zinc serves as an effector of coagulation, anticoagulation and fibrinolysis. Zinc binds numerous plasma proteins and modulates their structure and function. Because activated platelets secrete zinc into the local microenvironment, the concentration of zinc increases in the vicinity of a thrombus. Consequently, the role of zinc varies depending on the microenvironment; a feature that endows zinc with the capacity to spatially and temporally regulate haemostasis and thrombosis. This paper reviews the mechanisms by which zinc regulates coagulation, platelet aggregation, anticoagulation and fibrinolysis and outlines how zinc serves as a ubiquitous modulator of haemostasis and thrombosis.

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.

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

Aim: C1-INH-HAE is caused by activation of plasma kallikrein which subsequently cleaves high-molecular-weight kininogen (HMWK) to generate bradykinin and cHMWK. Materials & methods: A novel ion-pair 2D LC–MS/MS assay was developed to measure the 46 kDa 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. Results: The LLOQ was 200 ng/ml. The overall cHMWK recovery combining crash and digestion was 57.5%. The precision of the method was ≤12.7% and accuracy ≤-13.8%. Conclusion: A reagent-free LC–MS assay has been developed for the quantitation of 46 kDa 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.

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

Essentials Kallikrein amplifies contact activation and is a potential target for preventing thrombosis. We developed and characterized a kallikrein aptamer using convergent evolution and kinetic assays. Kall1-T4 prolongs intrinsic clotting time by inhibiting factor XIIa-mediated prekallikrein activation. Kall1-T4 decreases high-molecular-weight kininogen cleavage and bradykinin release.

SUMMARY

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.

G Protein-Coupled Kinin Receptors and Immunity Against Pathogens

For decades, immunologists have considered the complement system as a paradigm of a proteolytic cascade that, acting cooperatively with the immune system, enhances host defense against infectious organisms. In recent years, advances made in thrombosis research disclosed a functional link between activated neutrophils, monocytes, and platelet-driven thrombogenesis. Forging a physical barrier, the fibrin scaffolds generated by synergism between the extrinsic and intrinsic (contact) pathways of coagulation entrap microbes within microvessels, limiting the systemic spread of infection while enhancing the clearance of pathogens by activated leukocytes. Insight from mice models of thrombosis linked fibrin formation via the intrinsic pathway to the autoactivation of factor XII (FXII) by negatively charged "contact" substances, such as platelet-derived polyphosphates and DNA from neutrophil extracellular traps. Following cleavage by FXIIa, activated plasma kallikrein (PK) initiates inflammation by liberating the nonapeptide bradykinin (BK) from an internal domain of high molecular weight kininogen (HK). Acting as a paracrine mediator, BK induces vasodilation and increases microvascular permeability via activation of endothelial B2R, a constitutively expressed subtype of kinin receptor. During infection, neutrophil-driven extravasation of plasma fuels inflammation via extravascular activation of the kallikrein-kinin system (KKS). Whether liberated by plasma-borne PK, tissue kallikrein, and/or microbial-derived proteases, the short-lived kinins activate immature dendritic cells via B2R, thus linking the infection-associated innate immunity/inflammation to the adaptive arm of immunity. As inflammation persists, a GPI-linked carboxypeptidase M removes the C-terminal arginine from the primary kinin, converting the B2R agonist into a high-affinity ligand for B1R, a GPCR subtype that is transcriptionally upregulated in injured/inflamed tissues. As reviewed here, lessons taken from studies of kinin receptor function in experimental infections have shed light on the complex proteolytic circuits that, acting at the endothelial interface, reciprocally couple immunity to the proinflammatory KKS.

The role of the complement system in hereditary angioedema

Hereditary angioedema (HAE) is a rare, but potentially life-threatening disorder, characterized by acute, recurring, and self-limiting edematous episodes of the face, extremities, trunk, genitals, upper airways, or the gastrointestinal tract. HAE may be caused by the deficiency of C1-inhibitor (C1-INH-HAE) but another type of the disease, hereditary angioedema with normal C1-INH function (nC1-INH-HAE) was also described. The patient population is quite heterogeneous as regards the location, frequency, and severity of edematous attacks, presenting large intra- and inter-individual variation. Here, we review the role of the complement system in the pathomechanism of HAE and also present an overview on the complement parameters having an importance in the diagnosis or in predicting the severity of HAE.

Unveiling the participation of avian kinin ornithokinin and its receptors in the chicken inflammatory response

Vasoactive peptides are key early mediators of inflammation released through activation of different enzymatic systems. The mammalian kinin-kallikrein (K-KLK) system produces bradykinin (BK) through proteolytic cleavage of a kininogen precursor by enzymes named kallikreins. BK acts through specific ubiquitous G-protein coupled receptors (B1R and B2R) to participate in physiological processes and inflammatory responses, such as activation of mononuclear phagocytes. In chickens, the BK-like nonapeptide ornithokinin (OK) has been shown to promote intracellular calcium increase in embryonic fibroblasts and to be vasodilatory in vivo. Also, one of its receptors (B2R) was already cloned. However, the participation of chicken K-KLK system components in the inflammatory response remains unknown and was therefore investigated. We first showed that B1R, B2R and kininogen 1 (KNG1) are expressed in unstimulated chicken tissues and macrophages. We next showed that chicken B1R and B2R are expressed at transcript and protein levels in chicken macrophages and are upregulated by E. coli LPS or avian pathogenic E. coli (APEC) infection. Interestingly, exogenous OK induced internalization and degradation of OK receptors protein, notably B2R. Also, OK induced intracellular calcium increase and potentiated zymosan-induced ROS production and Dextran-FITC endocytosis by chicken macrophages. Exogenous OK itself did not promote APEC killing and had no pro-inflammatory effect. However, when combined with LPS or APEC, OK upregulated cytokine/chemokine gene expression and NO production by chicken macrophages. This effect was not blocked by canonical non-peptide B1R or B2R receptor antagonists but was GPCR- and PI3K/Akt-dependent. In vivo, pulmonary colibacillosis led to upregulation of OK receptors expression in chicken lungs and liver. Also, colibacillosis led to significant upregulation of OK precursor KNG1 expression in liver and in cultured hepatocytes (LMH). We therefore provide hitherto unknown information on how OK and its receptors are involved in inflammation and infection in chickens.

The effects of nanomaterials on blood coagulation in hemostasis and thrombosis

The blood coagulation balance in the organism is achieved by the interaction of the blood platelets (PLTs) with the plasma coagulation system (PCS) and the vascular endothelial cells. In healthy organism, these systems prevent thrombosis and, in events of vascular damage, enable blood clotting to stop bleeding. The dysregulation of hemostasis may cause serious thrombotic and/or hemorrhagic pathologies. Numerous engineered nanomaterials are being investigated for biomedical purposes and are unavoidably exposed to the blood. Also, nanomaterials may access vascular system after occupational, environmental, or other types of exposure. Thus, it is essential to evaluate the effects of engineered nanomaterials on hemostasis. This review focuses on investigations of nanomaterial interactions with the blood components involved in blood coagulation: the PCS and PLTs. Particular emphases include the pathophysiology of effects of nanomaterials on the PCS, including the kallikrein-kinin system, and on PLTs. Methods for investigating these interactions are briefly described, and a review of the most important studies on the interactions of nanomaterials with plasma coagulation and platelets is provided. WIREs Nanomed Nanobiotechnol 2017, 9:e1448. doi: 10.1002/wnan.1448 For further resources related to this article, please visit the WIREs website.

The initiation and effects of plasma contact activation: an overview

The plasma contact system sits atop the intrinsic coagulation cascade and plasma kallikrein-kinin pathway, and in vivo its activation contributes, respectively, to coagulation and inflammation mainly via two downstream pathways. This system has been widely investigated, its activation mechanisms by negatively charged surfaces and the interactions within its components, factor XII, prekallikrein and high molecular weight kininogen are well understood at the biochemical level. However, as most of the activators that have been discovered by in vitro experiments are exogenous, the physiological activators and roles of the contact system have remained unclear and controversial. In the last two decades, several physiological activators have been identified, and a better understanding of its roles and its connection with other signaling pathways has been obtained from in vivo studies. In this article, we present an overview of the contact pathway with a focus on the activation mechanisms, natural stimuli, possible physiological roles, potential risks of its excessive activation, remaining questions and future prospects.

Blood coagulation factor XII drives adaptive immunity during neuroinflammation via CD87-mediated modulation of dendritic cells

Aberrant immune responses represent the underlying cause of central nervous system (CNS) autoimmunity, including multiple sclerosis (MS). Recent evidence implicated the crosstalk between coagulation and immunity in CNS autoimmunity. Here we identify coagulation factor XII (FXII), the initiator of the intrinsic coagulation cascade and the kallikrein-kinin system, as a specific immune cell modulator. High levels of FXII activity are present in the plasma of MS patients during relapse. Deficiency or pharmacologic blockade of FXII renders mice less susceptible to experimental autoimmune encephalomyelitis (a model of MS) and is accompanied by reduced numbers of interleukin-17A-producing T cells. Immune activation by FXII is mediated by dendritic cells in a CD87-dependent manner and involves alterations in intracellular cyclic AMP formation. Our study demonstrates that a member of the plasmatic coagulation cascade is a key mediator of autoimmunity. FXII inhibition may provide a strategy to combat MS and other immune-related disorders.

Kallikrein Promotes Inflammation in Human Dental Pulp Cells Via Protease-Activated Receptor-1

Plasma kallikrein (KLKB1), a serine protease, cleaves high-molecular weight kininogen to produce bradykinin, a potent vasodilator and pro-inflammatory peptide. In addition, KLKB1 activates plasminogen and other leukocyte and blood coagulation factors and processes pro-enkephalin, prorenin, and C3. KLKB1 has also been shown to cleave protease-activated receptors in vascular smooth muscle cells to regulate the expression of epidermal growth factor receptor. In this study, we investigated KLKB1-dependent inflammation and activation of protease-activated receptor-1 in human dental pulp cells. These cells responded to KLKB1 stimulation by increasing intracellular Ca(2+) , upregulating cyclooxygenase-2, and secreting prostaglandin E2 . Remarkably, SCH79797, an antagonist of protease-activated receptor-1, blocked these effects. Thus, these data indicate that KLKB1 induces inflammatory reactions in human dental tissues via protease-activated receptor 1. J. Cell. Biochem. 117: 1522-1528, 2016. © 2015 Wiley Periodicals, Inc.

Proteolytic degradation of neuropeptide Y (NPY) from head to toe: Identification of novel NPY-cleaving peptidases and potential drug interactions in CNS and Periphery

The bioactivity of neuropeptide Y (NPY) is either N-terminally modulated with respect to receptor selectivity by dipeptidyl peptidase 4 (DP4)-like enzymes or proteolytic degraded by neprilysin or meprins, thereby abrogating signal transduction. However, neither the subcellular nor the compartmental differentiation of these regulatory mechanisms is fully understood. Using mass spectrometry, selective inhibitors and histochemistry, studies across various cell types, body fluids, and tissues revealed that most frequently DP4-like enzymes, aminopeptidases P, secreted meprin-A (Mep-A), and cathepsin D (CTSD) rapidly hydrolyze NPY, depending on the cell type and tissue under study. Novel degradation of NPY by cathepsins B, D, L, G, S, and tissue kallikrein could also be identified. The expression of DP4, CTSD, and Mep-A at the median eminence indicates that the bioactivity of NPY is regulated by peptidases at the interphase between the periphery and the CNS. Detailed ex vivo studies on human sera and CSF samples recognized CTSD as the major NPY-cleaving enzyme in the CSF, whereas an additional C-terminal truncation by angiotensin-converting enzyme could be detected in serum. The latter finding hints to potential drug interaction between antidiabetic DP4 inhibitors and anti-hypertensive angiotensin-converting enzyme inhibitors, while it ablates suspected hypertensive side effects of only antidiabetic DP4-inhibitors application. The bioactivity of neuropeptide Y (NPY) is either N-terminally modulated with respect to receptor selectivity by dipeptidyl peptidase 4 (DP4)-like enzymes or proteolytic degraded by neprilysin or meprins, thereby abrogating signal transduction. However, neither the subcellular nor the compartmental differentiation of these regulatory mechanisms is fully understood. Using mass spectrometry, selective inhibitors and histochemistry, studies across various cell types, body fluids, and tissues revealed that most frequently DP4-like enzymes, aminopeptidases P, secreted meprin-A (Mep-A), and cathepsin D (CTSD) rapidly hydrolyze NPY, depending on the cell type and tissue under study. Novel degradation of NPY by cathepsins B, D, L, G, S, and tissue kallikrein could also be identified. The expression of DP4, CTSD, and Mep-A at the median eminence indicates that the bioactivity of NPY is regulated by peptidases at the interphase between the periphery and the CNS. Detailed ex vivo studies on human sera and CSF samples recognized CTSD as the major NPY-cleaving enzyme in the CSF, whereas an additional C-terminal truncation by angiotensin-converting enzyme could be detected in serum. The latter finding hints to potential drug interaction between antidiabetic DP4 inhibitors and anti-hypertensive angiotensin-converting enzyme inhibitors, while it ablates suspected hypertensive side effects of only antidiabetic DP4-inhibitors application.

[Kallikrein-Kinin System. Long History and Present. (To 90th Anniversary of Discovery of the System)]

The kallikrein-kinin system (KKS) is the key proteolytic system participating in control of a wide spectrum of physiological functions and the development of many pathological conditions. This explains great interest in structures, functions and molecular biology of separate components of the system, molecular mechanisms of their interaction and relationship with other regulatory systems. The information in this field for the last two decades clarifies the role of KKS in morphogenesis of cells, regulation of smooth muscular contractility of some organs, decrease of blood pressure, increase of vascular permeability, the development of inflammation, transformation of cells and the other functions of both physiological and pathological processes. Essential progress in understanding of functions KKS was made by the discovery and study of bradykinin receptors, cloning of kininogen and kallikrein encoding genes, revealing of domain structure of kininogen, prekallikrein and some kininases and decoding of mechanisms of contact phase of proteolytic system activation in blood plasma.

Polyphosphate as modulator of hemostasis, thrombosis, and inflammation

Inorganic polyphosphate (polyP), a linear polymer of phosphates, is present in many infectious microorganisms and is secreted by mast cells and platelets. PolyP has recently been shown to accelerate blood clotting and slow fibrinolysis, in a manner that is highly dependent on polymer length. Very long-chain polyP (of the type present in microorganisms) is an especially potent trigger of the contact pathway, enhances the proinflammatory activity of histones, and may participate in host responses to pathogens. PolyP also inhibits complement, providing another link between polyP and inflammation/innate immunity. Platelet-size polyP (which is considerably shorter) accelerates factor V activation, opposes the anticoagulant action of tissue factor pathway inhibitor, modulates fibrin clot structure, and promotes factor XI activation. PolyP may have utility in treating bleeding. It is also a potential target for the development of antithrombotic drugs with a novel mechanism of action and potentially fewer bleeding side effects compared with conventional anticoagulants.

Reincarnation of ancient links between coagulation and complement

Throughout evolution, organisms have developed means to contain wounds by simultaneously limiting bleeding and eliminating pathogens and damaged host cells via the recruitment of innate defense mechanisms. Disease emerges when there is unchecked activation of innate immune and/or coagulation responses. A key component of innate immunity is the complement system. Concurrent excess activation of coagulation and complement - two major blood-borne proteolytic pathways - is evident in numerous diseases, including atherosclerosis, diabetes, venous thromboembolic disease, thrombotic microangiopathies, arthritis, cancer, and infectious diseases. Delineating the cross-talk between these two cascades will uncover novel therapeutic insights.

How it all starts: Initiation of the clotting cascade

The plasma coagulation system in mammalian blood consists of a cascade of enzyme activation events in which serine proteases activate the proteins (proenzymes and procofactors) in the next step of the cascade via limited proteolysis. The ultimate outcome is the polymerization of fibrin and the activation of platelets, leading to a blood clot. This process is protective, as it prevents excessive blood loss following injury (normal hemostasis). Unfortunately, the blood clotting system can also lead to unwanted blood clots inside blood vessels (pathologic thrombosis), which is a leading cause of disability and death in the developed world. There are two main mechanisms for triggering the blood clotting, termed the tissue factor pathway and the contact pathway. Only one of these pathways (the tissue factor pathway) functions in normal hemostasis. Both pathways, however, are thought to contribute to thrombosis. An emerging concept is that the contact pathway functions in host pathogen defenses. This review focuses on how the initiation phase of the blood clotting cascade is regulated in both pathways, with a discussion of the contributions of these pathways to hemostasis versus thrombosis.

Critical insights into the beneficial and protective actions of the kallikrein-kinin system

Hypertension is characterized by an imbalance between the renin-angiotensin system (RAS) and the kallikrein-kinin system (KKS). Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II AT-1 receptor antagonists (also known as sartans or ARBs) are potent modulators of these systems and are highly effective as first-line treatments for hypertension, diabetic nephropathies, and diseases of the brain and coronary arteries. However, these agents are mechanistically distinct and should not be considered interchangeable. In this mini-review, we provide novel insights into the often neglected roles of the KKS in the beneficial, protective, and reparative actions of ACEIs. Indeed, ACEIs are the only antihypertensive drugs that properly reduce the imbalance between the RAS and the KKS, thereby restoring optimal cardiovascular homeostasis and significantly reducing morbidity and the risk of all-cause mortality among individuals affected by hypertension and other cardiovascular diseases.

Pathophysiology of Hereditary Angioedema

The genetic deficiency of the C1 inhibitor is responsible for hereditary angioedema (HAE), which is a disease transmitted as an autosomal dominant trait. More than 200 point mutations in the C1 inhibitor gene have been found to be associated with HAE. Patients with this disease suffer from recurrent angioedema, which is mediated by bradykinin derived from activation of the contact system. This system is physiologically controlled at several steps by the C1 inhibitor. In this review, we describe known mechanisms for the development of angioedema in patients with C1 inhibitor deficiency.

Novel mechanism of plasma prekallikrein (PK) activation by vascular smooth muscle cells: evidence of the presence of PK activator

The contribution of plasma prekallikrein (PK) to vascular remodeling is becoming increasingly recognized. Plasma PK is activated when the zymogen PK is digested to an active enzyme by activated factor XII (FXII). Here, we present our findings that vascular smooth muscle cells (VSMC) activate plasma PK in the absence of FXII. Extracted plasma membrane and cytosolic fractions of VSMCs activate PK, but the rate of PK activation was greater by the membrane fraction. FXII neutralizing antibody did not affect PK activation by extracted proteins of VSMCs. VSMC PKA was inhibited by the serine protease inhibitors such as aprotinin, phenylmethylsulfonyl fluoride, leupeptin and CTI with CI50 of 0.78 μM, 1 mM, 3.13 μM and 40 nM on the cultured cells, respectively. No inhibition of PK activation by cysteine, aspartic acid, and metalloprotease inhibitors was observed. This is the first report of the presence of an intrinsic PKA in VSMC. Considering that VSMCs are normally separated from the circulating blood by endothelial cells, direct PK activation by VSMCs may play a role in disease states like diabetes, hyperlipidemia or hypertension where the endothelial layer is damaged.

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

BACKGROUND

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSION

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

The Kallikrein Inhibitor from Bauhinia bauhinioides (BbKI) shows antithrombotic properties in venous and arterial thrombosis models

The Bauhinia bauhinioides Kallikrein Inhibitor (BbKI) is a Kunitz-type serine peptidase inhibitor of plant origin that has been shown to impair the viability of some tumor cells and to feature a potent inhibitory activity against human and rat plasma kallikrein (Kiapp 2.4 nmol/L and 5.2 nmol/L, respectively). This inhibitory activity is possibly responsible for an effect on hemostasis by prolonging activated partial thromboplastin time (aPTT). Because the association between cancer and thrombosis is well established, we evaluated the possible antithrombotic activity of this protein in venous and arterial thrombosis models. Vein thrombosis was studied in the vena cava ligature model in Wistar rats, and arterial thrombosis in the photochemical induced endothelium lesion model in the carotid artery of C57 black 6 mice. BbKI at a concentration of 2.0 mg/kg reduced the venous thrombus weight by 65% in treated rats in comparison to rats in the control group. The inhibitor prolonged the time for total artery occlusion in the carotid artery model mice indicating that this potent plasma kallikrein inhibitor prevented thrombosis.

Bradykinin analysis revived--a validated method for determination of its stable metabolite in whole blood by LC-MS/MS

Investigation of bradykinin involvement in diseases like hereditary angioedema has been greatly hindered by its rapid metabolism and generation, induced by sampling. Because of this, reliable measurements of bradykinin have yet to be introduced in clinical practice. Prevention of bradykinin generation during sampling, and determination of the in vivo generated stable metabolite BK1-5, should allow a reliable indirect measure of bradykinin involvement. An LC-MS/MS method has been developed to determine BK1-5 in human whole blood. The method inactivates metabolizing enzymes with ethanol, followed by solid phase extraction (C18), separation (C8) and detection (linear ion trap) through the transitions 287.25→320.20 (y3, quantifier), 408.20 (b4, qualifier) for BK1-5, and 292.17→330.20 (y3, quantifier), 408.20 (b4, qualifier) for the heavy labelled internal standard. The method showed acceptable linearity (n=3, r(2)=0.994), intra-run precision (CV<15%), inter-run precision (CV<15%) and accuracy (CV<14%), without matrix effects. LLOQ was 265.5 pmol L(-1) and LOD was 35.4 pmol L(-1). The method was used on blood samples from patients with hereditary angioedema, where BK1-5 was measured during attacks and in remision. The samples showed elevated concentrations (up to 1.7 nmol L(-1) during attacks and 265.5 pmol L(-1) in remission) compared to healthy volunteers (<35.4 pmol L(-1)). This is the first time BK1-5 in hereditary angioedema patients has been measured.

The kallikrein-kinin system as a regulator of cardiovascular and renal function

Autocrine, paracrine, endocrine, and neuroendocrine hormonal systems help regulate cardio-vascular and renal function. Any change in the balance among these systems may result in hypertension and target organ damage, whether the cause is genetic, environmental or a combination of the two. Endocrine and neuroendocrine vasopressor hormones such as the renin-angiotensin system (RAS), aldosterone, and catecholamines are important for regulation of blood pressure and pathogenesis of hypertension and target organ damage. While the role of vasodepressor autacoids such as kinins is not as well defined, there is increasing evidence that they are not only critical to blood pressure and renal function but may also oppose remodeling of the cardiovascular system. Here we will primarily be concerned with kinins, which are oligopeptides containing the aminoacid sequence of bradykinin. They are generated from precursors known as kininogens by enzymes such as tissue (glandular) and plasma kallikrein. Some of the effects of kinins are mediated via autacoids such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), and/or tissue plasminogen activator (tPA). Kinins help protect against cardiac ischemia and play an important part in preconditioning as well as the cardiovascular and renal protective effects of angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARB). But the role of kinins in the pathogenesis of hypertension remains controversial. A study of Utah families revealed that a dominant kallikrein gene expressed as high urinary kallikrein excretion was associated with a decreased risk of essential hypertension. Moreover, researchers have identified a restriction fragment length polymorphism (RFLP) that distinguishes the kallikrein gene family found in one strain of spontaneously hypertensive rats (SHR) from a homologous gene in normotensive Brown Norway rats, and in recombinant inbred substrains derived from these SHR and Brown Norway rats this RFLP cosegregated with an increase in blood pressure. However, humans, rats and mice with a deficiency in one or more components of the kallikrein-kinin-system (KKS) or chronic KKS blockade do not have hypertension. In the kidney, kinins are essential for proper regulation of papillary blood flow and water and sodium excretion. B2-KO mice appear to be more sensitive to the hypertensinogenic effect of salt. Kinins are involved in the acute antihypertensive effects of ACE inhibitors but not their chronic effects (save for mineralocorticoid-salt-induced hypertension). Kinins appear to play a role in the pathogenesis of inflammatory diseases such as arthritis and skin inflammation; they act on innate immunity as mediators of inflammation by promoting maturation of dendritic cells, which activate the body's adaptive immune system and thereby stimulate mechanisms that promote inflammation. On the other hand, kinins acting via NO contribute to the vascular protective effect of ACE inhibitors during neointima formation. In myocardial infarction produced by ischemia/reperfusion, kinins help reduce infarct size following preconditioning or treatment with ACE inhibitors. In heart failure secondary to infarction, the therapeutic effects of ACE inhibitors are partially mediated by kinins via release of NO, while drugs that activate the angiotensin type 2 receptor act in part via kinins and NO. Thus kinins play an important role in regulation of cardiovascular and renal function as well as many of the beneficial effects of ACE inhibitors and ARBs on target organ damage in hypertension.

Endothelial cell permeability during hantavirus infection involves factor XII-dependent increased activation of the kallikrein-kinin system

Hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS) are diseases caused by hantavirus infections and are characterized by vascular leakage due to alterations of the endothelial barrier. Hantavirus-infected endothelial cells (EC) display no overt cytopathology; consequently, pathogenesis models have focused either on the influx of immune cells and release of cytokines or on increased degradation of the adherens junction protein, vascular endothelial (VE)-cadherin, due to hantavirus-mediated hypersensitization of EC to vascular endothelial growth factor (VEGF). To examine endothelial leakage in a relevant in vitro system, we co-cultured endothelial and vascular smooth muscle cells (vSMC) to generate capillary blood vessel-like structures. In contrast to results obtained in monolayers of cultured EC, we found that despite viral replication in both cell types as well as the presence of VEGF, infected in vitro vessels neither lost integrity nor displayed evidence of VE-cadherin degradation. Here, we present evidence for a novel mechanism of hantavirus-induced vascular leakage involving activation of the plasma kallikrein-kinin system (KKS). We show that incubation of factor XII (FXII), prekallikrein (PK), and high molecular weight kininogen (HK) plasma proteins with hantavirus-infected EC results in increased cleavage of HK, higher enzymatic activities of FXIIa/kallikrein (KAL) and increased liberation of bradykinin (BK). Measuring cell permeability in real-time using electric cell-substrate impedance sensing (ECIS), we identified dramatic increases in endothelial cell permeability after KKS activation and liberation of BK. Furthermore, the alterations in permeability could be prevented using inhibitors that directly block BK binding, the activity of FXIIa, or the activity of KAL. Lastly, FXII binding and autoactivation is increased on the surface of hantavirus-infected EC. These data are the first to demonstrate KKS activation during hantavirus infection and could have profound implications for treatment of hantavirus infections.

Primary manifestations of disease due to hantavirus infections include systemic vascular leakage and hypotension for which the underlying mechanism is not known. A particularly perplexing finding is that the vascular endothelium remains intact during hantavirus infection and with no apparent cytopathic effects to explain leakage and edema. Our studies show for the first time that hantavirus-infected EC have increased KKS activation resulting in liberation of the inflammatory peptide, BK. BK is a potent inducer of vascular permeability, edema formation, and hypotension; thus, our results provide a novel mechanism for hantavirus-induced vascular abnormalities. Additionally, we describe the use of an in vitro capillary blood vessel model to examine responses occurring locally in blood vessels during infection. This model could be used in future studies by others for assessing further aspects of hantavirus pathogenesis or that of other vascular tropic viruses.

The arrestin-selective angiotensin AT1 receptor agonist [Sar1,Ile4,Ile8]-AngII negatively regulates bradykinin B2 receptor signaling via AT1-B2 receptor heterodimers

The renin-angiotensin and kallikrein-kinin systems are key regulators of vascular tone and inflammation. Angiotensin II, the principal effector of the renin-angiotensin system, promotes vasoconstriction by activating angiotensin AT1 receptors. The opposing effects of the kallikrein-kinin system are mediated by bradykinin acting on B1 and B2 bradykinin receptors. The renin-angiotensin and kallikrein-kinin systems engage in cross-talk at multiple levels, including the formation of AT1-B2 receptor heterodimers. In primary vascular smooth muscle cells, we find that the arrestin pathway-selective AT1 agonist, [Sar(1),Ile(4),Ile(8)]-AngII, but not the neutral AT1 antagonist, losartan, inhibits endogenous B2 receptor signaling. In a transfected HEK293 cell model that recapitulates this effect, we find that the actions of [Sar(1),Ile(4), Ile(8)]-AngII require the AT1 receptor and result from arrestin-dependent co-internalization of AT1-B2 heterodimers. BRET50 measurements indicate that AT1 and B2 receptors efficiently heterodimerize. In cells expressing both receptors, pretreatment with [Sar(1),Ile(4),Ile(8)]-AngII blunts B2 receptor activation of Gq/11-dependent intracellular calcium influx and Gi/o-dependent inhibition of adenylyl cyclase. In contrast, [Sar(1),Ile(4),Ile(8)]-AngII has no effect on B2 receptor ligand affinity or bradykinin-induced arrestin3 recruitment. Both radioligand binding assays and quantitative microscopy-based analysis demonstrate that [Sar(1),Ile(4),Ile(8)]-AngII promotes internalization of AT1-B2 heterodimers. Thus, [Sar(1),Ile(4),Ile(8)]-AngII exerts lateral allosteric modulation of B2 receptor signaling by binding to the orthosteric ligand binding site of the AT1 receptor and promoting co-sequestration of AT1-B2 heterodimers. Given the opposing roles of the renin-angiotensin and kallikrein-kinin systems in vivo, the distinct properties of arrestin pathway-selective and neutral AT1 receptor ligands may translate into different pharmacologic actions.

Prekallikrein deficiency

Nurses often encounter abnormal laboratory assays that require them to investigate further to ensure that appropriate patient care is provided. A prolonged activated partial thromboplastin time (PTT) with a normal prothrombin time (PT) assay demand further examination, to rule out laboratory error or bleeding disorders. Prekallikrein deficiency is a rare coagulation deficiency that presents itself with a prolonged PTT and a normal PT. It was first identified in 4 of the 11 Fletcher family children in 1965, coincidentally when one of the Fletcher children was undergoing a workup for an adenoidectomy. Both the Fletcher parents had normal coagulation laboratory assays with no history of bleeding tendencies. The term Fletcher factor deficiency was used until Fletcher factor was later identified as plasma prekallikrein. A prekallikrein deficiency is inherited as an autosomal recessive trait. The purpose of this article is to provide a basic review for nurses on hemostasis, identify the 6 causes of a prolonged PTT with a normal or slightly prolonged PT, and to present 2 recently diagnosed adult cases, not previously reported in the medical literature.

Hereditary angioedema therapy: kallikrein inhibition and bradykinin receptor antagonism

Current strategies for the treatment of hereditary angioedema (HAE) include targeted inhibition or antagonism of the contact system, which is dysregulated in HAE patients by a C1 esterase inhibitor deficiency. Ecallantide, a plasma kallikrein inhibitor, and icatibant, a selective bradykinin-2 receptor antagonist, have recently been evaluated in clinical studies for the treatment of acute HAE attacks. Both drugs have demonstrated evidence of efficacy and safety in treating acute HAE episodes, with ecallantide approved for use in the United States and icatibant approved for use in Europe. As therapeutic options for HAE expand for both for prophylactic and acute treatment strategies, a number of patient-specific and drug-specific factors have emerged as important considerations when developing individualized HAE management plans. Optimization of HAE therapy will require further integration of new therapies into the current treatment paradigm.

Polyphosphate: an ancient molecule that links platelets, coagulation, and inflammation

Inorganic polyphosphate is widespread in biology and exhibits striking prohemostatic, prothrombotic, and proinflammatory effects in vivo. Long-chain polyphosphate (of the size present in infectious microorganisms) is a potent, natural pathophysiologic activator of the contact pathway of blood clotting. Medium-chain polyphosphate (of the size secreted from activated human platelets) accelerates factor V activation, completely abrogates the anticoagulant function of tissue factor pathway inhibitor, enhances fibrin clot structure, and greatly accelerates factor XI activation by thrombin. Polyphosphate may have utility as a hemostatic agent, whereas antagonists of polyphosphate may function as novel antithrombotic/anti-inflammatory agents. The detailed molecular mechanisms by which polyphosphate modulates blood clotting reactions remain to be elucidated.

Modulation of C1-Inhibitor and Plasma Kallikrein Activities by Type IV Collagen

The contact system of coagulation can be activated when in contact with biomaterials. As collagen is being tested in novel biomaterials in this study, we have investigated how type IV collagen affects plasma kallikrein and C1-inhibitor. Firstly, we showed C1-inhibitor binds to type IV collagen with a Kd of 0.86 μM. The effects of type IV collagen on plasma kallikrein, factor XIIa, and β-factor XIIa activity and on C1-inhibitor function were determined. Factor XIIa rapidly lost activity in the presence of type IV collagen, whereas plasma kallikrein and β-factor XIIa were more stable. The rate of inhibition of plasma kallikrein by C1-inhibitor was decreased by type IV collagen in a dose-dependent manner. These studies could be relevant to the properties of biomaterials, which contain collagen, and should be considered in the testing for biocompatibility.

Factor VII-activating protease is activated in multiple trauma patients and generates anaphylatoxin C5a

Severe tissue injury results in early activation of serine protease systems including the coagulation and complement cascade. In this context, little is known about factor VII-activating protease (FSAP), which is activated by substances released from damaged cells such as histones and nucleosomes. Therefore, we have measured FSAP activation in trauma patients and have identified novel FSAP substrates in human plasma. Mass spectrometry-based methods were used to identify FSAP binding proteins in plasma. Anaphylatoxin generation was measured by ELISA, Western blotting, protein sequencing, and chemotaxis assays. Plasma samples from trauma patients were analyzed for FSAP Ag and activity, nucleosomes, C5a, and C3a. Among others, we found complement components C3 and C5 in FSAP coimmunoprecipitates. C3 and C5 were cleaved by FSAP in a dose- and time-dependent manner generating functional C3a and C5a anaphylatoxins. Activation of endogenous FSAP in plasma led to increased C5a generation, but this was not the case in plasma of a homozygous carrier of Marburg I single nucleotide polymorphism with lower FSAP activity. In multiple trauma patients there was a large increase in circulating FSAP activity and nucleosomes immediately after the injury. A high correlation between FSAP activity and C5a was found. These data suggest that activation of FSAP by tissue injury triggers anaphylatoxin generation and thereby modulates the posttraumatic inflammatory response in vivo. A strong link between C5a, nucleosomes, and FSAP activity indicates that this new principle might be important in the regulation of inflammation.

Thrombin and vascular inflammation

Vascular endothelium is a key regulator of homeostasis. In physiological conditions it mediates vascular dilatation, prevents platelet adhesion, and inhibits thrombin generation. However, endothelial dysfunction caused by physical injury of the vascular wall, for example during balloon angioplasty, acute or chronic inflammation, such as in atherothrombosis, creates a proinflammatory environment which supports leukocyte transmigration toward inflammatory sites. At the same time, the dysfunction promotes thrombin generation, fibrin deposition, and coagulation. The serine protease thrombin plays a pivotal role in the coagulation cascade. However, thrombin is not only the key effector of coagulation cascade; it also plays a significant role in inflammatory diseases. It shows an array of effects on endothelial cells, vascular smooth muscle cells, monocytes, and platelets, all of which participate in the vascular pathophysiology such as atherothrombosis. Therefore, thrombin can be considered as an important modulatory molecule of vascular homeostasis. This review summarizes the existing evidence on the role of thrombin in vascular inflammation.

Activation of the contact system at the surface of Fusobacterium necrophorum represents a possible virulence mechanism in Lemièrre's syndrome

Fusobacterium necrophorum causes Lemièrre's syndrome, a serious disease with septic thrombophlebitis of the internal jugular vein, pulmonary involvement, and systemic inflammation. The contact system is a link between inflammation and coagulation, and contact activation by the bacteria could therefore contribute to the abnormal coagulation and inflammation seen in patients with Lemièrre's syndrome. In this study, F. necrophorum was found to bind radiolabeled high-molecular-weight kininogen (HK), a central component of the contact system. Binding was inhibited by the addition of unlabeled HK and domain D5 of HK but not other components of the contact system, indicating a specific interaction mediated through the D5 region. Binding of HK was significantly reduced after pretreatment of the bacteria with trypsin, suggesting that surface proteins are involved in HK binding. Incubation of the bacteria with human plasma resulted in an HK breakdown pattern suggestive of bradykinin release, and bradykinin was also detected in the supernatant. In addition, we show that factor XI (FXI), another component of the contact system, binds to F. necrophorum and that the bound FXI reconstitutes the activated partial thromboplastin time of FXI-deficient plasma. Thrombin activity was detected at the surface of the bacteria following incubation with plasma, indicating that the intrinsic pathway of coagulation is activated at the surface. This activity was completely blocked by inhibitors of the contact system. The combined results show that the contact system is activated at the surface of F. necrophorum, suggesting a pathogenic role for this system in Lemièrre's syndrome.

High molecular weight kininogen activates B2 receptor signaling pathway in human vascular endothelial cells

The nonenzymatic cofactor high molecular weight kininogen (HK) is a precursor of bradykinin (BK). The production of BK from HK by plasma kallikrein has been implicated in the pathogenesis of inflammation and vascular injury. However, the functional role of HK in the absence of prekallikrein (PK), the proenzyme of plasma kallikrein, on vascular endothelial cells is not fully defined. In addition, no clinical abnormality is seen in PK-deficient patients. Therefore, an investigation into the effect of HK, in the absence of PK, on human pulmonary artery endothelial cell (HPAEC) function was performed. HK caused a marked and dose-dependent increase in the intracellular calcium [Ca(2+)](i) level in HPAEC. Gd(3+) and verapamil potentiated the HK-induced increase in [Ca(2+)](i). HK-induced Ca(2+) increase stimulated endothelial nitric oxide (NO) and prostacyclin (PGI(2)) production. The inhibitors of B(2) receptor-dependent signaling pathway impaired HK-mediated signal transduction in HPAEC. HK had no effect on endothelial permeability at physiological concentration. This study demonstrated that HK regulates endothelial cell function. HK could play an important role in maintaining normal endothelial function and blood flow and serve as a cardioprotective peptide.

The kallikrein-kinin system as a regulator of cardiovascular and renal function

Autocrine, paracrine, endocrine, and neuroendocrine hormonal systems help regulate cardio-vascular and renal function. Any change in the balance among these systems may result in hypertension and target organ damage, whether the cause is genetic, environmental or a combination of the two. Endocrine and neuroendocrine vasopressor hormones such as the renin-angiotensin system (RAS), aldosterone, and catecholamines are important for regulation of blood pressure and pathogenesis of hypertension and target organ damage. While the role of vasodepressor autacoids such as kinins is not as well defined, there is increasing evidence that they are not only critical to blood pressure and renal function but may also oppose remodeling of the cardiovascular system. Here we will primarily be concerned with kinins, which are oligopeptides containing the aminoacid sequence of bradykinin. They are generated from precursors known as kininogens by enzymes such as tissue (glandular) and plasma kallikrein. Some of the effects of kinins are mediated via autacoids such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), and/or tissue plasminogen activator (tPA). Kinins help protect against cardiac ischemia and play an important part in preconditioning as well as the cardiovascular and renal protective effects of angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARB). But the role of kinins in the pathogenesis of hypertension remains controversial. A study of Utah families revealed that a dominant kallikrein gene expressed as high urinary kallikrein excretion was associated with a decreased risk of essential hypertension. Moreover, researchers have identified a restriction fragment length polymorphism (RFLP) that distinguishes the kallikrein gene family found in one strain of spontaneously hypertensive rats (SHR) from a homologous gene in normotensive Brown Norway rats, and in recombinant inbred substrains derived from these SHR and Brown Norway rats this RFLP cosegregated with an increase in blood pressure. However, humans, rats and mice with a deficiency in one or more components of the kallikrein-kinin-system (KKS) or chronic KKS blockade do not have hypertension. In the kidney, kinins are essential for proper regulation of papillary blood flow and water and sodium excretion. B2-KO mice appear to be more sensitive to the hypertensinogenic effect of salt. Kinins are involved in the acute antihypertensive effects of ACE inhibitors but not their chronic effects (save for mineralocorticoid-salt-induced hypertension). Kinins appear to play a role in the pathogenesis of inflammatory diseases such as arthritis and skin inflammation; they act on innate immunity as mediators of inflammation by promoting maturation of dendritic cells, which activate the body's adaptive immune system and thereby stimulate mechanisms that promote inflammation. On the other hand, kinins acting via NO contribute to the vascular protective effect of ACE inhibitors during neointima formation. In myocardial infarction produced by ischemia/reperfusion, kinins help reduce infarct size following preconditioning or treatment with ACE inhibitors. In heart failure secondary to infarction, the therapeutic effects of ACE inhibitors are partially mediated by kinins via release of NO, while drugs that activate the angiotensin type 2 receptor act in part via kinins and NO. Thus kinins play an important role in regulation of cardiovascular and renal function as well as many of the beneficial effects of ACE inhibitors and ARBs on target organ damage in hypertension.

Procoagulant properties of bare and highly PEGylated vinyl-modified silica nanoparticles

AIMS

Undesired alterations of the blood clotting balance may follow the intravascular injection of nanotherapeutics/diagnostics. Here, we tested the procoagulant activity of synthetic amorphous silica (SAS) and organically modified silica (ORMOSIL) nanoparticles (NPs) and whether a high-density polyethylene glycol coating minimizes these effects.

MATERIALS & METHODS

Hageman factor- and tissue factor-dependent activation of human blood/plasma coagulation, and binding to human monocytes, endothelial cells and platelets were quantified in vitro using naked and PEGylated ORMOSIL-NPs. Their effects were compared with those of SAS-NPs, present in many industrial products, and of poly(lactic-co-glycolic acid)- and small unilamellar vesicles-NPs, already approved for use in humans.

RESULTS

Both SAS-NPs and ORMOSIL-NPS presented a significant procoagulant activity. However, highly PEGylated ORMOSIL-NPs were particularly averse to the interaction with the soluble factors and cellular elements that may lead to intravascular blood coagulation.

CONCLUSION

Stealth, highly PEGylated ORMOSIL-NPs with a poor procoagulant activity can be used as starting blocks to design hemocompatible nanomedical-devices.