Metal ion binding to anticoagulation factor II from the venom of Agkistrodon acutus: stabilization of the structure and regulation of the binding affinity to activated coagulation factor X

Anticoagulation factor II (ACF II) isolated from the venom of Agkistrodon acutus is an activated coagulation factor X (FXa)-binding protein with both anticoagulant and hypotensive activities. The thermodynamics of the binding of alkaline earth metal ions to ACF II and their effects on the stability of ACF II and the binding of ACF II to FXa were investigated by isothermal titration calorimetry, fluorescence, differential scanning calorimetry, and surface plasmon resonance. The binding of ACF II to FXa does not have an absolute requirement for Ca(2+). Mg(2+), Sr(2+), and Ba(2+) can induce the binding of ACF II to FXa. The radii of the cations bound in ACF II crucially affect the binding affinity of ACF II for cations and the structural stability of ACF II against guanidine hydrochloride and thermal denaturation, whereas the radii of cations bound in FXa markedly affect the binding affinity between ACF II and FXa. The binding affinities of ACF II for cations and the capacities of metal-induced stabilization of ACF II follow the same trend: Ca(2+) > Sr(2+) > Ba(2+). The metal-induced binding affinities of ACF II for FXa follow the trend Mg(2+) > Ca(2+) > Sr(2+) > Ba(2+). Although Mg(2+) shows significantly low binding affinity with ACF II, Mg(2+) is the most effective to induce the binding of ACF II with FXa. Our observations suggest that in blood the bindings of Ca(2+) in two sites of ACF II increase the structural stability of ACF II, but these bindings are not essential for the binding of ACF II with FXa, and that the binding of Mg(2+) and Ca(2+) to FXa may be essential for the recognition between FXa and ACF II. Like Ca(2+), the abundant Mg(2+) in blood also plays an important role in the anticoagulation of ACF II.

Requirements for receptor engagement during infection by adenovirus complexed with blood coagulation factor X

Human adenoviruses from multiple species bind to coagulation factor X (FX), yet the importance of this interaction in adenovirus dissemination is unknown. Upon contact with blood, vectors based on adenovirus serotype 5 (Ad5) binds to FX via the hexon protein with nanomolar affinity, leading to selective uptake of the complex into the liver and spleen. The Ad5:FX complex putatively targets heparan sulfate proteoglycans (HSPGs). The aim of this study was to elucidate the specific requirements for Ad5:FX-mediated cellular uptake in this high-affinity pathway, specifically the HSPG receptor requirements as well as the role of penton base-mediated integrin engagement in subsequent internalisation. Removal of HS sidechains by enzymatic digestion or competition with highly-sulfated heparins/heparan sulfates significantly decreased FX-mediated Ad5 cell binding in vitro and ex vivo. Removal of N-linked and, in particular, O-linked sulfate groups significantly attenuated the inhibitory capabilities of heparin, while the chemical inhibition of endogenous HSPG sulfation dose-dependently reduced FX-mediated Ad5 cellular uptake. Unlike native heparin, modified heparins lacking O- or N-linked sulfate groups were unable to inhibit Ad5 accumulation in the liver 1h after intravascular administration of adenovirus. Similar results were observed in vitro using Ad5 vectors possessing mutations ablating CAR- and/or α(v) integrin binding, demonstrating that attachment of the Ad5:FX complex to the cell surface involves HSPG sulfation. Interestingly, Ad5 vectors ablated for α(v) integrin binding showed markedly delayed cell entry, highlighting the need for an efficient post-attachment internalisation signal for optimal Ad5 uptake and transport following surface binding mediated through FX. This study therefore integrates the established model of α(v) integrin-dependent adenoviral infection with the high-affinity FX-mediated pathway. This has important implications for mechanisms that define organ targeting following contact of human adenoviruses with blood.

Effects of temperature, pH, and inhibitors on the procoagulant characterization of FIa, a factor X activator from the venom of Daboia russellii siamensis (Myanmar)

FIa, a factor X activator, was isolated from the venom of Daboia russellii siamensis (Myanmar) after a series of chromatographic separations. FIa displayed procoagulant activity by shortening plasma recalcification time and converted human factor X (FX) to activated human factor X (FXa) by cleaving the heavy FX chain, possibly at the Arg51-Ile52 peptide. FIa was positive in a glycoprotein staining test, demonstrating that it is a glycoprotein. Optimal temperature and pH values were important for FIa procoagulant activity. Procoagulant activity was maintained above 85% of the initial activity at pH 7.0 approximately 8.0, and showed equally maximum activity at temperatures ranging from 30 to 50 degrees C. In addition, FIa procoagulant activity was completely inhibited by EDTA (5 mM), but not by PMSF (10 mM), suggesting that it is a metalloproteinase.

Platelet tissue factor synthesis in type 2 diabetic patients is resistant to inhibition by insulin

OBJECTIVE

Patients with type 2 diabetes have an increased risk of cardiovascular disease and show abnormalities in the coagulation cascade. We investigated whether increased synthesis of tissue factor (TF) by platelets could contribute to the hypercoagulant state.

RESEARCH DESIGN AND METHODS

Platelets from type 2 diabetic patients and matched control subjects were adhered to different surface-coated proteins, and TF premRNA splicing, TF protein, and TF procoagulant activity were measured.

RESULTS

Different adhesive proteins induced different levels of TF synthesis. A mimetic of active clopidogrel metabolite (AR-C69931 MX) reduced TF synthesis by 56 +/- 10%, an aspirin-like inhibitor (indomethacin) by 82 +/- 9%, and the combination by 96 +/- 2%, indicating that ADP release and thromboxane A(2) production followed by activation of P2Y12 and thromboxane receptors mediate surface-induced TF synthesis. Interference with intracellular pathways revealed inhibition by agents that raise cAMP and interfere with phosphatidylinositol 3-kinase/protein kinase B. Insulin is known to raise cAMP in platelets and inhibited collagen III-induced TF premRNA splicing and reduced TF activity by 35 +/- 5 and 47 +/- 5% at 1 and 100 nmol/l. Inhibition by insulin was reduced in type 2 diabetes platelets resulting in an approximately 1.6-fold higher TF synthesis than in matched control subjects.

CONCLUSIONS

We characterized the extra- and intracellular mechanisms that couple surface activation to TF synthesis in adhering platelets. In healthy individuals, TF synthesis is inhibited by insulin, but in patients with type 2 diabetes inhibition is impaired. This leads to the novel finding that platelets from type 2 diabetic patients produce more TF than platelets from matched control subjects.

Functional role of O-linked and N-linked glycosylation sites present on the activation peptide of factor X

BACKGROUND

There are two O-linked and two N-linked glycosylation sites on the activation peptide of factor X (FX) involving residues Thr-17, Thr-29, Asn-39 and Asn-49.

OBJECTIVES

The purpose of this study was to explore the contribution of carbohydrates of the FX activation peptide to zymogen recognition by physiological activators.

METHODS

The putative glycosylation sites were substituted individually or in combinations with Ala and mutants were expressed in mammalian cells. The entire activation peptide up to the P3 residue was deleted in another construct.

RESULTS

It was discovered that activation of zymogen mutants by both FVIIa and FIXa on negatively charged phospholipid vesicles has been improved 2-40-fold independent of a cofactor. These mutants were activated with slightly lower catalytic efficiency (k(cat)/K(m)) by FVIIa in the extrinsic Xase complex, though both K(m) and k(cat) constants for mutants were elevated. With the exception of approximately 3-fold improvement in the activation of N49A, the catalytic efficiency of FIXa toward mutants was decreased 2-5-fold in the intrinsic Xase complex.

CONCLUSIONS

The carbohydrate chains of the FX activation peptide play an important role in restricting the specificity of zymogen recognition by both FVIIa and FIXa, thereby preventing the cofactor-independent activation of FX by these proteases. On the other hand, the carbohydrates contribute to the cofactor-dependent recognition of the zymogen by both extrinsic and intrinsic Xase complexes.

Plasmin immunization preferentially induces potentially prothrombotic IgG anticardiolipin antibodies in MRL/MpJ mice

OBJECTIVE

To test the hypothesis, utilizing 2 experimental mouse models, that plasmin is an important autoantigen that drives the production of certain IgG anticardiolipin (aCL) antibodies in patients with the antiphospholipid syndrome.

METHODS

BALB/cJ and MRL/MpJ mice were immunized with Freund's complete adjuvant in the presence or absence of human plasmin. The mouse sera were analyzed for production of IgG antiplasmin, IgG aCL, and IgG anti-beta(2)-glycoprotein I (anti-beta(2)GPI) antibodies. IgG monoclonal antibodies (mAb) were generated from the plasmin-immunized MRL/MpJ mice with high titers of aCL, and these 10 mAb were studied for their binding properties and functional activity in vitro.

RESULTS

Plasmin-immunized BALB/cJ mice produced high titers of IgG antiplasmin only, while plasmin-immunized MRL/MpJ mice produced high titers of IgG antiplasmin, IgG aCL, and IgG anti-beta(2)GPI. Both strains of mice immunized with the adjuvant alone did not develop IgG antiplasmin or IgG aCL. All 10 of the IgG mAb bound to human plasmin and cardiolipin, while 4 of 10 bound to beta(2)GPI, 3 of 10 bound to thrombin, and 4 of 10 bound to the activated coagulation factor X (FXa). Functionally, 4 of the 10 IgG mAb inhibited plasmin activity, 1 of 10 hindered inactivation of thrombin by antithrombin III, and 2 of 10 inhibited inactivation of FXa by antithrombin III.

CONCLUSION

Plasmin immunization leads to production of IgG antiplasmin, aCL, and anti-beta(2)GPI in MRL/MpJ mice, but leads to production of only IgG antiplasmin in BALB/cJ mice. IgG mAb generated from plasmin-immunized MRL/MpJ mice bind to various antigens and exhibit procoagulant activity in vitro. These results suggest that plasmin may drive potentially prothrombotic aCL in genetically susceptible individuals.

Cloning and comparison of factor X from rhesus monkey (Macaca mulatta)

The reliability of the rhesus monkey as an important experimental animal depends on its genetic concordance with human. During our assessment of the rhesus monkey as a preclinical model for coagulation-related research, we cloned the full-length cDNA of rhesus monkey factor X (FX) and compared its genetic characteristics and coagulation activity with those of human FX. The full-length cDNA of rhesus monkey FX was 1683 bp in length, corresponding to 487 coding amino acids and sharing 94.71% nucleotide identity and 93.65% amino acid identity with human FX. When FX sequences from different animals were compared with that of human FX, rhesus monkey and baboon FX showed similar degrees of homology to human FX, which were less than that between human and chimpanzee FX sequences but remarkably higher than those of another 2 monkey species, bovine, pig, and rodents. Comparison of functional sites between human and rhesus monkey FX revealed high similarities between their amino acids sequences and 3-dimensional structures. The average coagulation activity of FX from 24 rhesus monkeys was in the normal range of that of healthy humans. The rhesus monkey therefore may be a suitable animal model for research addressing coagulation factor X.

Factor IX mutants with enhanced catalytic activity

BACKGROUND

Activated coagulation factor IX (FIXa) has low catalytic activity towards its physiologic substrate FX when activated FVIII (FVIIIa) is absent. One reason for this is that the FIX surface loop 99 stabilizes FIXa in a conformation that limits access of FX to the active site.

OBJECTIVES

To investigate the effect of mutations in loop 99 and in the active site on FIXa activity with and without FVIIIa.

METHODS

Five full-length FIX mutants with amino acid exchanges in the catalytic domain of FIX were constructed and characterized by measuring their activity in FX activation in model systems and in plasma.

RESULTS AND CONCLUSIONS

The mutants showed no or marginally improved catalytic properties in FX activation by the intrinsic tenase complex (FIXa-FVIIIa-Ca(2+)-phospholipid). The combination of mutations Y94F and K98T hardly affected FX activation in the presence of FVIIIa, but yielded a FIX molecule that, in FIX-depleted plasma, had approximately 2.5-fold higher clotting activity and approximately 3.5-fold higher activity in a thrombin generation assay than plasma-derived FIX (pdFIX). Two FIXa mutants had considerably increased activities towards FX in the absence of FVIIIa. FIXa-Y94F/K98T/Y177F/I213V/E219G (FIXa-L) and FIXa-Y94F/A95aK/K98T/Y177F/I213V/E219G (FIXa-M) activated FX with catalytic efficiencies (k(cat)/K(m)) that, as compared with activated pdFIX, were increased 17-fold and six-fold, respectively. However, in plasma, their zymogen forms performed similarly to pdFIX. This indicates that the introduced mutations not only affected the activity of FIXa but may have also influenced the lifetime of the activated mutant molecules in plasma by modifying their activation and/or inhibition rates.

Use of chromogenic assay of factor X to accept or reject INR results in Warfarin treated patients

A warfarin treated patient unexpectedly presented with an elevated international normalized ratio (INR). Repeat testing in two laboratories gave conflicting results. The chromogenic assay of factor X was used to determine the correct INR result. The patient had laboratory results consistent with a dysfibrinogenemia, which prevented detection of the endpoint with a photo-optical detection system. The chromogenic assay of factor X is recommended for monitoring patients on warfarin when the INR cannot be accurately determined due to interference with the fibrin endpoint in the INR.

Peptidomic analysis of blood plasma after in vivo treatment with protease inhibitors--a proof of concept study

Native peptides can be regarded as surrogate markers for protease activity in biological samples. Analysis of peptides by peptidomics allows to monitor protease activity in vivo and to describe the influence of protease inhibition. To elucidate the potential of peptides as markers for in vivo protease inhibition we analyzed plasma samples from animals treated with either the indirect FXa inhibitor FONDAPARINUX or the dipeptidylpeptidase IV inhibitor AB192. Signals correlating with the treatment were subsequently identified and assessed with respect to protease-dependent consensus cleavage motifs and occurrence of downstream targets. It could be shown that regulated peptides were either substrates, products or downstream targets of the inhibited protease. The results from the present study demonstrate that the in vivo analysis of peptides by peptidomics has the potential to broaden the knowledge of inhibitor related effects in vivo and that this method may pave the way to develop predictive biomarkers.

Coagulation abnormalities in liver disease

The decreased capacity of the liver to synthesize proteins is the main cause of decreased blood levels of clotting factors II, V, VII, IX, X and of antithrombin III in patients with liver disease. Therefore, determination of the activity or concentration of these coagulation proteins is a useful test of liver function and guide to prognosis, provided that other mechanisms which may influence the blood level are carefully considered. Clotting factor assays have an only limited value for the differential diagnosis in liver disease.

Procoagulant activities of plasma factor VIIc and factor Xc are positively and independently associated with concentrations of the high-density lipoprotein apolipoprotein, apo A-II

The pro- and antiatherogenic roles of apolipoproteins B and A-I, respectively, are well-established although the importance of apolipoprotein A-II remains unclear. There is extensive evidence for the involvement of plasma lipoproteins in haemostatic function. However, in-vivo studies of relationships between haemostatic variables and apolipoprotein concentrations are very limited. Plasma fibrinogen, factors VIIc and Xc (FVIIc and FXc, respectively), apolipoproteins (apo) A-I, A-II and B, triglycerides, total, low-density and high-density lipoprotein (HDL) cholesterol, and cholesterol in HDL subfractions 2 and 3 were measured in 186 apparently healthy Caucasian men (aged 26-78 years; body mass index 19.9-37.8 kg/m(2)). Associations between haemostatic, apolipoprotein, lipid and lipoprotein variables were explored in uni- and multivariable analyses. Fibrinogen did not correlate with any of the lipid-related variables. FVIIc and FXc were significant positive univariate correlates of total cholesterol (correlation coefficients 0.26, p<0.001 and 0.19, p<0.05, respectively) triglycerides (0.37, p<0.001 and 0.36, p<0.001), and apoB (0.21, p<0.01 and 0.17, p<0.05) and apoA-II (0.19, p<0.05 and 0.29, p<0.001). HDL(2) subfraction cholesterol correlated negatively with FVIIc and FXc (-0.20, p<0.01 and -0.22, p<0.01, respectively). In multivariable analysis, only the associations of FVIIc and FXc with total cholesterol, triglycerides and apoA-II remained statistically significant. In conclusion, total cholesterol and triglycerides were the major independent lipid correlates of FVIIc and FXc. The independent and positive associations of apoA-II with FVIIc and FXc suggest a prothrombotic involvement for this apolipoprotein.

Blood coagulation and fibrinolysis in male patients with hypogonadotropic hypogonadism: plasma factor V and factor X activities increase in hypogonadotropic hypogonadism

BACKGROUND AND OBJECTIVES

In men, androgens have both pro- and anti-thrombotic effects. Androgen deficiency in men is associated with an increased incidence of cardiovascular disease (CVD). However, the influence of hypogonadism on hemostasis is controversial. Little is known about hemostatic features of male patients with idiopathic hypogonadotropic hypogonadism (IHH). Thus, the aim of the present study was to evaluate the markers of endogenous coagulation and fibrinolysis, and to investigate the relationships between endogenous sex hormones and hemostatic parameters and serum lipid profile in men with IHH.

DESIGN AND METHODS

Seventeen patients with IHH and 20 age-matched healthy controls were included in the study. Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, factors (F) V, VII, VIII, IX, and X activities, von Willebrand factor (vWF), antithrombin III (AT III), protein C, protein S, tissue plasminogen activator (t-PA), and tissue plasminogen activator inhibitor (PAI-1), as well as common lipid variables, were measured. The relationships between serum sex hormones and these hemostatic parameters were examined.

RESULTS

Compared with the control subjects, platelet count, FV, FX, and protein C activities were significantly increased in patients with IHH (p<0.01, p<0.05, p<0.01, and p<0.05, respectively), whereas AT III was decreased (p<0.05). Fibrinogen, FVIII, vWF, t-PA, PAI-1, and the other coagulation/fibrinolysis parameters and lipid profile in patients with IHH were not different from the controls. In patients with IHH, we showed that serum LH level was negatively correlated with fibrinogen (r: -0.78, p<0.01) and protein C (r: -0.55, p<0.05) and positively correlated with t-PA (r: 0.53, p<0.05). Serum FSH levels inversely correlated with fibrinogen (r: -0.75, p<0.01).

INTERPRETATION AND CONCLUSIONS

We found some differences in the hemostatic parameters between the patients with IHH and healthy controls. Increased platelet count, FV and FX activities and decreased AT III levels in patients with IHH represent a potential hypercoagulable state, which might augment the risk for atherosclerotic and atherothrombotic complications. Therefore, IHH may be associated with an increased risk of CVD. However, sex hormones may play a role at different levels of the complex hemostatic system in patients with IHH.

Rat prostate tumors express cancer procoagulant, an activator of coagulation factor X

Two common procoagulant activities associated with tumors are tissue factor and cancer procoagulant (CP), an activator of coagulation factor X. We have identified a convenient source of CP in transplanted Lobund-Wistar rat PA3 prostate tumors. CP activity was purified from 5 independent transplanted prostate tumors by column chromatography. The protein activated factor X in the absence of TF and factor VII. An antihuman CP antibody recognized rat CP in an ELISA and inactivated CP activity in a chromogenic assay. Lobund-Wistar prostate tumors may provide a convenient animal model useful in determining the role of CP in cancer development.

Heparanase modulates heparinoids anticoagulant activities via non-enzymatic mechanisms

A key element for the physiological restriction of blood coagulation at the endothelial cell surface is its non-thrombogenic property, mainly attributed to cell surface heparan sulfate proteoglycans. Heparanase is an endo-beta-D-glucuronidase with specific heparan sulfate degrading activity, which is produced and stored in platelets, and is released upon their activation. We examined the effects of heparanase pro-enzyme on coagulation functions, predominantly under physiological conditions. While heparanase pro-enzyme does not directly affect coagulation protein activities, it has profound effects on heparinoid-mediated regulation of coagulation responses, apparently via mechanisms that do not involve its enzymatic activity. Heparanase pro-enzyme reverses the anti-coagulant activity of unfractionated heparin on the coagulation pathway as well as on thrombin activity. In addition, heparanase pro-enzyme abrogated the factor X inhibitory activity of low-molecular-weight heparin (LMWH). The pro-coagulant effects of the non-active heparanase were also exerted by its major functional heparin-binding peptide. Finally, the effects of heparanase on the activity of factor VII activating protease that is auto-activated by heparinoids indicated a complete antagonistic action of heparanase in this system. Altogether, heparanase pro-coagulant activities that were also demonstrated in plasma samples from patients under LMWH treatment, point to a possible use of this molecule as antagonist for heparinoid treatment.

Purification and partial characterizations of coagulant protein FIa from Daboia russelli siamensis (Myanmar) venom

AIM

To purify and characterize the coagulant protein FIa from Daboia russelli siamensis (Myanmar) venom.

METHODS

FIa was purified from Daboia russelli siamensis (Myanmar) venom by ion-exchange chromatography on CM-Sephadex C-50, and gel filtration on Sephadex G-75 and a Superdex 75 column. The hemostatic activity of FIa was determined by the method of Williams and Esnouf. The specific chromogenic substrates were used respectively to determine the activation of factor X and prothrombin. The fibrinogen-clotting activity of FIa was determined by the method of Gao et al. Normal saline was used as a negative control while factor Xa and thrombin were used as positive controls, respectively.

RESULTS

FIa, a coagulant protein, was achieved by ion-exchange chromatography and gel filtration with a molecular weight of 34,479 and an isoelectric point of 7.2. FIa was shown to have strong hemostatic activity. The hemostatic activity of 0.5 mg FIa was equal to that of 1.5625 u thrombin. FIa primarily activated factor X, however, had no influence on prothrombin, nor did it cleave or clot fibrinogen.

CONCLUSION

FIa is a factor X-activating enzyme, which could activate factor X to factor Xa, but has no effect on prothrombin and fibrinogen.

Fibrin formation by wounded bronchial epithelial cell layers in vitro is essential for normal epithelial repair and independent of plasma proteins

BACKGROUND

The bronchial epithelium is in contact with, and continually damaged by, the environment. Animal models have indicated that normal epithelial repair is rapid and supported by the formation of a provisional fibrin matrix that is exclusively plasma-derived.

OBJECTIVES

Our objectives were to demonstrate the ability of normal human bronchial epithelial (NHBE) cells to produce coagulation cascade proteins and form fibrin in response to damage, independently of plasma proteins, and to show that formation of a cross-linked fibrin matrix is essential for normal epithelial repair in vitro.

METHODS

Primary NHBE cells and cells of the 16HBE 14o- bronchial epithelial cell line were grown and maintained in vitro prior to mechanical wounding of confluent monolayers in serum-free media. Tissue factor (TF) and factor XIII (FXIII) were visualized on 16HBE 14o- monolayers using immunohistochemistry. The time-dependent expression of TF, factor VII (FVII), factor X (FX), fibrinogen, soluble fibrin, FXIII subunit A (FXIIIA) and D-dimers following wounding of confluent 16HBE 14o- monolayers was investigated using immunoassays. TF and FVII expression at the mRNA level was investigated by RT-PCR. The role of coagulation cascade proteins in the repair response of NHBE and 16HBE 14o- monolayers was investigated using neutralizing antibodies.

RESULTS

Active TF was constitutively expressed in 16HBE 14o- cells. Levels of FVII, FX, fibrinogen, soluble fibrin, FXIIIA and D-dimers in culture supernatants increased rapidly and were maximal 20 min after wounding the monolayers. Expression of TF and FVII mRNA was significantly increased 10 and 4 h, respectively, after wounding. Neutralizing antibodies to TF, fibrinogen and FXIIIA significantly inhibited repair of NHBE and 16HBE 14o- cell layers.

CONCLUSIONS

The bronchial epithelium has the potential to respond rapidly to mechanical damage by forming a cross-linked fibrin matrix that is essential for normal epithelial repair, independently of plasma proteins.

Major coagulation disturbances during fractionated plasma separation and adsorption

Fractionated Plasma Separation and Adsorption (FPSA) is a novel nonbiologic detoxification system for the removal of protein-bound solutes. FPSA is used to bridge patients during fulminant liver failure, either to functional recovery or to liver transplantation. Besides liver failure associated protein bound solutes, several important uremic retention solutes share important protein binding. We observed repeated occlusive thrombosis of the arterio-venous conduit during FPSA in hemodialysis (HD) patients, resulting in acute loss of function. A major reduction of several coagulation factors was demonstrated, exceeding 50% for factor II, factor X and protein C. Broad disturbances of the coagulation system were confirmed in FPSA treated liver failure patients. An ex vivo recirculation model demonstrated nonspecific adsorption of coagulation factors protein S and protein C on the anion exchange cartridge. Direct contact between fractionated plasma and the Prometh02 anion exchanger causes significant adsorption of procoagulant and anti-coagulant factors, associated with clinically relevant adverse events.