Kallikrein activates prothrombin

Plasma Kallikrein as a Forgotten Clotting Factor

For decades, it was considered that plasma kallikrein's (PKa) sole function within the coagulation cascade is the activation of factor (F)XII. Until recently, the two key known activators of FIX within the coagulation cascade were activated FXI(a) and the tissue factor-FVII(a) complex. Simultaneously, and using independent experimental approaches, three groups identified a new branch of the coagulation cascade, whereby PKa can directly activate FIX. These key studies identified that (1) FIX or FIXa can bind with high affinity to either prekallikrein (PK) or PKa; (2) in human plasma, PKa can dose dependently trigger thrombin generation and clot formation independent of FXI; (3) in FXI knockout murine models treated with intrinsic pathway agonists, PKa activity results in increased formation of FIXa:AT complexes, indicating direct activation of FIX by PKa in vivo. These findings suggest that there is both a canonical (FXIa-dependent) and non-canonical (PKa-dependent) pathway of FIX activation. These three recent studies are described within this review, alongside historical data that hinted at the existence of this novel role of PKa as a coagulation clotting factor. The implications of direct PKa cleavage of FIX remain to be determined physiologically, pathophysiologically, and in the context of next-generation anticoagulants in development.

Blood Kallikrein-8 and Non-Amnestic Mild Cognitive Impairment: An Exploratory Study

Background: Blood kallikrein-8 is supposed to be a biomarker for mild cognitive impairment (MCI) due to Alzheimer’s disease (AD), a precursor of AD dementia. Little is known about the association of kallikrein-8 and non-AD type dementias. Objective: To investigate whether blood kallikrein-8 is elevated in individuals with non-amnestic MCI (naMCI), which has a higher probability to progress to a non-AD type dementia, compared with cognitively unimpaired (CU) controls. Methods: We measured blood kallikrein-8 at ten-year follow-up (T2) in 75 cases and 75 controls matched for age and sex who were participants of the population-based Heinz Nixdorf Recall study (baseline: 2000–2003). Cognitive performance was assessed in a standardized manner at five (T1) and ten-year follow-up. Cases were CU or had subjective cognitive decline (SCD) at T1 and had naMCI at T2. Controls were CU at both follow-ups. The association between kallikrein-8 (per 500 pg/ml increase) and naMCI was estimated using conditional logistic regression: odds ratios (OR) and 95% confidence intervals (95% CI) were determined, adjusted for inter-assay variability and freezing duration. Results: Valid kallikrein-8 values were measured in 121 participants (45% cases, 54.5% women, 70.5±7.1 years). In cases, the mean kallikrein-8 was higher than in controls (922±797 pg/ml versus 884±782 pg/ml). Kallikrein-8 was not associated with having naMCI compared to being CU (adjusted; OR: 1.03 [95% CI: 0.80–1.32]). Conclusion: This is the first population-based study that shows that blood kallikrein-8 tends not to be elevated in individuals with naMCI compared with CU. This adds to the evidence of the possible AD specificity of kallikrein-8.

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

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

Is kallikrein-8 a blood biomarker for detecting amnestic mild cognitive impairment? Results of the population-based Heinz Nixdorf Recall study

BACKGROUND

Kallikrein-8 (KLK8) might be an early blood-biomarker of Alzheimer's disease (AD). We examined whether blood KLK8 is elevated in persons with amnestic mild cognitive impairment (aMCI) which is a precursor of AD, compared to cognitively unimpaired (CU) controls.

METHODS

Forty cases and 80 controls, matched by sex and age (± 3years), were participants of the longitudinal population-based Heinz Nixdorf Recall study (baseline: 2000-2003). Standardized cognitive performance was assessed 5 (T1) and 10 years after baseline (T2). Cases were CU at T1 and had incidental aMCI at T2. Controls were CU at T1 and T2. Blood KLK8 was measured at T2. Using multiple logistic regression the association between KLK8 in cases vs. controls was investigated by estimating odds ratios (OR) and 95% confidence intervals (95%CI), adjusted for inter-assay variability and freezing duration. Using receiver operating characteristic (ROC) analysis, the diagnostic accuracy of KLK8 was determined by estimating the area under the curve (AUC) and 95%CI (adjusted for inter-assay variability, freezing duration, age, sex).

RESULTS

Thirty-seven participants with aMCI vs. 72 CU (36.7%women, 71.0±8.0 (mean±SD) years) had valid KLK8 measurements. Mean KLK8 was higher in cases than in controls (911.6±619.8 pg/ml vs.783.1±633.0 pg/ml). Fully adjusted, a KLK8 increase of 500pg/ml was associated with a 2.68 (1.05-6.84) higher chance of having aMCI compared to being CU. With an AUC of 0.92 (0.86-0.97), blood KLK8 was a strong discriminator for aMCI and CU.

CONCLUSION

This is the first population-based study to demonstrate the potential clinical utility of blood KLK8 as a biomarker for incipient AD.

Kallikrein directly interacts with and activates Factor IX, resulting in thrombin generation and fibrin formation independent of Factor XI

Prekallikrein (PK) is a zymogen that is converted to kallikrein (PKa) by factor (F)XIIa. PK and FXII reciprocally activate each other; the resulting FXIIa initiates activation of the coagulation system via the cleavage of FXI to FXIa, which then activates FIX. This manuscript describes a novel high-affinity binding interaction between FIX(a) and PK(a) and reports that PKa can dose- and time-dependently activate FIX to generate FIXa, resulting in thrombin generation and clot formation independent of FXIa. Characterization of the kinetics of FIX activation reveal that PKa is a more significant activator of FIX than previously considered. This work highlights a new amendment to the coagulation cascade where PKa can directly activate FIX.

Kallikrein (PKa), generated by activation of its precursor prekallikrein (PK), plays a role in the contact activation phase of coagulation and functions in the kallikrein-kinin system to generate bradykinin. The general dogma has been that the contribution of PKa to the coagulation cascade is dependent on its action on FXII. Recently this dogma has been challenged by studies in human plasma showing thrombin generation due to PKa activity on FIX and also by murine studies showing formation of FIXa-antithrombin complexes in FXI deficient mice. In this study, we demonstrate high-affinity binding interactions between PK(a) and FIX(a) using surface plasmon resonance and show that these interactions are likely to occur under physiological conditions. Furthermore, we directly demonstrate dose- and time-dependent cleavage of FIX by PKa in a purified system by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and chromogenic assays. By using normal pooled plasma and a range of coagulation factor-deficient plasmas, we show that this action of PKa on FIX not only results in thrombin generation, but also promotes fibrin formation in the absence of FXII or FXI. Comparison of the kinetics of either FXIa- or PKa-induced activation of FIX suggest that PKa could be a significant physiological activator of FIX. Our data indicate that the coagulation cascade needs to be redefined to indicate that PKa can directly activate FIX. The circumstances that drive PKa substrate specificity remain to be determined.

Characterization of covalent protein modification by triclosan in vivo and in vitro via three-dimensional liquid chromatography-mass spectrometry: New insight into its adverse effects

Triclosan (TCS), an antimicrobial agent widely used in personal care products and ubiquitously exists in environment, has drawn increasing concern due to its potential to exert multiple adverse effects, ranging from endocrine disruption to carcinogenesis. However, the mechanism of these adverse effects is still not fully elucidated. More and more studies have shown that chemical reactive metabolites (RMs) covalently binding to proteins is a possible reason for these adverse effects, but there is still a lack of appropriate methods to predict or evaluate these adverse effects due to the extremely low abundance of the modified proteins in complex biological samples. In this study, we attempted to address this problem and investigate the possible mechanism of TCS adverse effects by a shotgun proteomics approach based on three-dimensional-liquid chromatography-mass spectrometry (3D-LC-MS). First, the in vitro incubation with model amino acids and protein in microsomes showed that TCS could react with cysteine residue of proteins through 3 types of RMs. Then, a 3D-LC-MS approach was developed to sensitively determine the low abundant modified proteins, which resulted in the identification of 45 TCS-modified proteins, including albumin, haptoglobin and NR1I2, in rats. STRING analysis indicated that these modified proteins mainly were involved in reproductive and development system, endocrine and immune system, and carcinogenesis, which were in accord with the main reported TCS-induced adverse effects and suggested that the covalent modification of TCS RMs for proteins might affect their activities and functions, thus inducing serious adverse effects. This study provided a new insight into the mechanism of TCS adverse effects and may serve as a valuable method to predict or evaluate adverse effects of ubiquitous chemicals.

Factor XII promotes blood coagulation independent of factor XI in the presence of long-chain polyphosphates

BACKGROUND

Inorganic polyphosphates (polyP), which are secreted by activated platelets (short-chain polyP) and accumulate in some bacteria (long-chain polyP), support the contact activation of factor XII (FXII) and accelerate the activation of FXI.

OBJECTIVES

The aim of the present study was to evaluate the role of FXI in polyP-mediated coagulation activation and experimental thrombus formation.

METHODS AND RESULTS

Pretreatment of plasma with antibodies that selectively inhibit FXI activation by activated FXII (FXIIa) or FIX) activation by activated FXI (FXIa) were not able to inhibit the procoagulant effect of long or short-chain polyP in plasma. In contrast, the FXIIa inhibitor, corn trypsin inhibitor, blocked the procoagulant effect of long and short polyP in plasma. In a purified system, long polyP significantly enhanced the rate of FXII and prekallikrein activation and the activation of FXI by thrombin but not by FXIIa. In FXI-deficient plasma, long polyP promoted clotting of plasma in an FIX-dependent manner. In a purified system, the activation of FXII and prekallikrein by long polyP promoted FIX activation and prothombin activation. In an ex vivo model of occlusive thrombus formation, inhibition of FXIIa with corn trypsin inhibitor but not of FXI with a neutralizing antibodies abolished the prothrombotic effect of long polyP.

CONCLUSIONS

We propose that long polyP promotes FXII-mediated blood coagulation bypassing FXI. Accordingly, some polyp-containing pathogens may have evolved strategies to exploit polyP-initiated FXII activation for virulence, and selective inhibition of FXII may improve the host response to pathogens.

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.

Glycosaminoglycans and activated contact system in cancer patient plasmas

Oncogenic mutations create cancer cells. Cancer cells require thrombin for growth, angiogenesis, and metastasis. All cancer patients display a hypercoagulable state, which includes platelet activation, blood coagulation, complement activation, vasodilatation, and inflammation. This often results in thrombosis, the second leading cause of death in cancer patients. It is established that chemically oversulfated glycosaminoglycans (GAGs) induce thrombin generation through contact system activation in human plasma. Thrombin is responsible for thrombosis. In this chapter, we show that plasmas from lung cancer patients contain activated contact systems apparent by the absence of high molecular weight kininogen and processed C1inh, by abnormal kallikrein and thrombin activities, and by increased glucosamine, galactosamine, and GAG levels. Activated contact systems were also evident in plasmas from breast, colon, and pancreatic cancer patients. These data suggest that GAGs or other molecules produced by tumors induce abnormal thrombin generation through contact system activation. Therefore, the contact system and glycans represent new targets for cancer diagnosis, prevention, and treatment.

Oversulfated Heparin By-Products Induce Thrombin Generation in Human Plasmas Through Contact System Activation

Thrombin generation is thought to be mediated predominantly by the tissue factor or ‘‘extrinsic’’ coagulation pathway. An alternate pathway to thrombin generation (the ‘‘intrinsic’’ pathway or contact system) has been observed when blood or plasma comes in contact with artificial surfaces. Here we present evidence for a new route to thrombin formation that begins with the activation of the contact system protein prekallikrein by oversulfated heparin (OS-HB). Kallikrein, instead of activated factor X, cleaves prothrombin to form thrombin. Thrombin then cleaves fibrinogen to form fibrin clots. Moreover, we show that OS-HB by-products induce kallikrein- and thrombin-like activities in normal human plasma and in human plasma devoid of coagulation factor X or downstream contact system components factor IX or factor XI. Oversulfated heparin by-product-induced thrombin generation may have had a role in the adverse reactions associated with the recent clinical use of contaminated heparin.

Life-threatening cardiac manifestations of primary antiphospholipid syndrome

We report a rare case of primary antiphospholipid syndrome (APS) in a 43-year-old man presenting as recurrent acute coronary stent thrombosis and complicated by three myocardial infarctions. As illustrated in this report, in APS patients recurrent life-threatening arterial thrombotic events may occur in spite of recommended anticoagulant therapy. We conclude that the APS should be considered as a potential cause of acute coronary syndrome, particularly in young individuals with a history of recurrent thrombotic events and/or with abnormal coagulation test results. Further studies are needed to determine the best therapeutic strategy for APS patients with acute coronary syndrome.

Fondaparinux and acute coronary syndromes: update on the OASIS 5-6 studies

Anticoagulant therapy is a major component in the management of acute coronary syndromes (ACS). Four anticoagulant agents are currently commercially available for ACS, namely unfractionated heparin (UFH), enoxaparin, bivalirudin and fondaparinux. We describe the advantages of fondaparinux and the reasons that have hampered its uptake into routine management of ACS. Fondaparinux was shown to be efficacious in the prevention of deep vein thrombosis vs low-molecular-weight heparins, while in the setting of venous thrombo-embolic disease, it was shown to be noninferior to enoxaparin and UFH. Two pivotal studies have demonstrated the efficacy of fondaparinux as an anticoagulant in the setting of ACS, namely OASIS-5 in non-ST elevation ACS, and OASIS-6 in ST elevation myocardial infarction (MI). In OASIS-5, fondaparinux was shown to be noninferior to enoxaparin in terms of death, MI or refractory ischemia at 9 days. Furthermore, a 50% reduction in bleeding complications was obtained with fondaparinux vs enoxaparin, leading to a risk reduction for death. In OASIS-6, fondaparinux was shown to be superior to the comparator (UFH or placebo). European and North American guidelines give fondaparinux a Grade 1A and 1B recommendation respectively, but uptake of fondaparinux in routine practice has been slow. We explore reasons for this, such as prevailing doubts about the efficacy of fondaparinux in the setting of angioplasty, the problem of catheter thrombosis, and the lack of antidote in case of bleeding complications. With the exception of primary angioplasty, fondaparinux is as effective as enoxaparin or UFH, but is also associated with a considerable reduction in bleeding complications, and thus, an undeniable net clinical benefit.

Activated contact system and abnormal glycosaminoglycans in lupus and other auto- and non-autoimmune diseases

Systemic lupus erythematosus (SLE), heparin-induced thrombocytopenia (HIT), rheumatoid arthritis (RA) are marked by the presence of autoantibodies against negatively changed DNA, phospholipids, heparin, and chondroitin sulfate, respectively. Heparin/protein complexes induce contact system activation in HIT patient plasmas. The activated contact system generates thrombin. Thrombin is responsible for thrombosis, a common cause of death and disabilities for both HIT and SLE. In this chapter, we analyze plasma contact system proteins, thrombin- and kallikrein-like activities, glucosamine and galactosamine content from SLE-, RA-, osteoarthritis (OA)-, and psoriasis (Ps)-patient plasmas in addition to pooled 30+ healthy patient plasmas. We found that all SLE patient plasmas exhibited abnormal contact systems marked by the absence of high molecular weight kininogen, the presence of processed C1 inhibitor (C1inh), the display of abnormal thrombin- and kallikrein-like activities, and increased levels of plasma glucosamine and galactosamine. Different patterns of contact system activation distinguish SLE, RA, and Ps whereas no contact system activation is observed in normal and OA patient plasmas. The presence of paradoxical "lupus anticoagulants" in certain thrombosis-prone SLE patient plasmas, marked by delayed clotting in clinical plasma test, was explained by the consumption of contact system proteins, especially high molecular weight kininogen. Finally, we discovered that mouse and human SLE autoantibodies bind to cell surface GAGs with structural selectivity. In conclusion, markers of abnormal contact system activation represent potential new targets for autoimmune disease diagnosis, prevention, and treatment. These markers might also be useful in monitoring SLE activity/severity and in pinpointing patients with SLE-associated arthritis and psoriasis.

Catheter thrombosis and percutaneous coronary intervention: fundamental perspectives on blood, artificial surfaces and antithrombotic drugs

Recent reports of catheter thrombosis among patients undergoing percutaneous coronary intervention (PCI) have had a significant impact on the development of new antithrombotic therapies. The overall incidence of this complication is unknown, mainly because of underreporting in contemporary clinical trials of coronary intervention. The etiology and pathophysiology of catheter thrombosis is also poorly understood. Introduction of a catheter or guidewire may not provoke the intense thrombotic response that follows angioplasty or stenting, but factors such as catheter materials and device size, equipment surface properties, flow conditions, procedural time and complexity, as well as the antiplatelet and anticoagulant drugs administered during the procedure influence the likelihood, rate and clinical impact of thrombosis. The crucial role of cellular interactions involving tissue-factor bearing cells and platelets in the process of thrombosis also needs to be critically explored when considering blood contact with an exogenous material. Focusing on the inherently prothrombotic environment of percutaneous coronary intervention, we review the physiologic underpinnings of catheter and guidewire thrombosis, and explore the effect of antithrombotic drugs at the interface between blood and material surfaces. We also propose a clinical classification for the diagnosis and investigation of catheter thrombosis in clinical trials of anticoagulant therapy and PCI.

Direct analysis reveals an absence of gamma-carboxyglutamic acid in cancer procoagulant from human tissues

Additional carboxylation of glutamic acid by vitamin K-dependent gamma-carboxylase is a common posttranslational modification of many proteins, including some of blood clotting factors. Vitamin K-antagonists, such as warfarin, are often included in the therapy of malignant disease, decreasing the blood coagulation potential. Cancer procoagulant, a direct blood coagulation factor X activator from malignant tissue, is considered as a vitamin K-dependent protein, so it could serve as one of possible targets for the therapy with warfarin. However, there is still no experimental data demonstrating directly the presence of gamma-carboxyglutamic acid (Gla) in a cancer procoagulant molecule. The presence of Gla in cancer procoagulant isolated from human amnion-chorion membranes and from human malignant melanoma WM 115 cell line was analyzed directly, using specific anti-Gla monoclonal antibodies. There was no detectable amount of Gla in cancer procoagulant isolated from fetal or malignant tissue. Cancer procoagulant from human tissues does not contain Gla-rich domain. The finding indicates that cancer procoagulant is rather a poor target for warfarin therapy of malignant disease.