Specific Determination of Plasmatic Thrombin Activity

Carbon dots doped with nitrogen as an ultrasensitive fluorescent probe for thrombin activity monitoring and inhibitor screening

A simple and sensitive fluorometric assay based on nitrogen-doped carbon dots (N-CDs) was developed for the determination of thrombin (TB) activity in human serum samples and living cells. The novel N-CDs were prepared by a facile one-pot hydrothermal method using 1,2-ethylenediamine and levodopa as precursors. Such N-CDs exhibited green fluorescence with excitation/emission peaks at 390/520 nm and a high fluorescence quantum yield of approximately 39.2%. H-D-Phenylalanyl-L-pipecolyl-Larginine-p-nitroaniline-dihydrochloride (S-2238) was hydrolyzed by TB to produce p-nitroaniline which was capable of quenching the fluorescence of N-CDs due to an inner filter effect. This assay was used to detect TB activity with a low detection limit of 11.3 fM. The proposed sensing method was then expanded to the TB inhibitor screening and exhibited excellent applicability. As a typical TB inhibitor, argatroban was determined in a concentration as low as 1.43 nM. The method has also been successfully employed for the determination of TB activity in living HeLa cells. This work showed significant potential for TB activity assay in clinical and biomedicine applications.

Controlled Decomposable Hydrogel Triggered with a Specific Enzyme

In this study, superabsorbent polyelectrolyte hydrogels were synthesized by cross-linking a nondegradable poly (allylamine hydrochloride) (PAH) and a recombinant protein with a specific enzymatic cleavage site. The recombinant protein was produced by E. coli with the pET-32b(+) plasmid, which is featured with the thioredoxin (Trx) gene containing a thrombin recognition site and a T7/lac hybrid promoter for high expression of recombinant protein. The swelling test shows that the composite hydrogel still maintained a high swelling ratio to 900% when 15% recombinant protein was cross-linked with PAH. The degradation test shows that such a PAH composite hydrogel could be decomposed by the addition of specific enzyme thrombin, which might lead to new biomedical applications of hydrogels needed to be decomposable by specific time not determined by the time period.

Comparison of hemostatic efficacy of topical Ankaferd Blood Stopper on heparinized and nonheparinized rats in bleeding related to liver injury

PURPOSE

In this study, hemostatic efficacy of Ankaferd Blood Stopper (ABS), a new generation hemostatic agent, was compared in the presence of heparin effect.

METHODS

Forty-eight Wistar albino rats were divided into two main groups as heparinized and nonheparinized, and these two main groupswere divided into six subgroups as control, Surgicel and ABS (n = 8). Grade 2 liver injury was performed on rats as standard. All groups were compared in terms of weight, laceration surface area, prothrombin time (PT), activated partial thromboplastin time (aPTT), international normalized ratio (INR), bleeding time, bleeding amount, hemoglobin (Hb) levels, macroscopic and microscopic reactions to the agent used.

RESULTS

Whereas there was no statistically significant difference between weight, laceration surface area, PT, INR and preoperative Hb values in the heparinized and nonheparinized groups, postoperative Hb, bleeding time, bleeding amount and aPTT values were statistically different (p < 0.05). In the heparin-hemostat interaction, the ABS group had the lowest bleeding in the heparinized group in terms of the amount of bleeding compared to the control and Surgicel groups (F = 0.764; p = 0.047). In macroscopic and microscopic comparison, there was no difference between the groups in terms of cell necrosis andfresh bleeding (p > 0.05), it was found that the Surgicel group had statistical significantly higher reaction scores (p < 0.05) than the other groups in terms of other parameters.

CONCLUSIONS

Ankaferd Blood Stopper can be safely and effectively used in surgical practice and in patients with additional diseases requiring heparinization, since it causes minimal reaction in the liver and decreases the amount of bleeding especially in the heparinized group.

Markers for neural degeneration and regeneration: novel highly sensitive methods for the measurement of thrombin and activated protein C in human cerebrospinal fluid

Inflammation and coagulation are tightly interconnected in the pathophysiology of neuronal diseases. Thrombin, a pro-coagulant serine protease is associated with neurodegeneration and its indirect inhibitor, activated protein C (aPC), is considered neuroprotective. While levels of thrombin and aPC activity are readily measured in the blood, similar assays in the cerebrospinal fluid (CSF) have not been described. The aim of this study was to establish a specific and sensitive enzymatic assay to measure both thrombin and aPC activity in the CSF. CSF was collected from 14 patients with suspected normal pressure hydrocephalus served as a control group, while seven patients with central nervous system infections served as an acute neuro-inflammatory study group and one sample of CSF following traumatic lumbar puncture served as a positive control. Thrombin and aPC activities were measured by fluorescence released by specific proteolytic cleavage in the presence of endopeptidase and amino-peptidase inhibitors to ensure specificity. Specificity of the method was verified by thrombin and serine-protease inhibitors N-alpha-((2-naphthylsulfinyl)glycyl)-DL-p-amidinophenylalanylpiperidine and phenylmethanesulfonyl fluoride. Inhibition of thrombin activity by CSF samples and levels of specific thrombin inhibitors were also assessed. Thrombin and aPC activities were reliably measured and were significantly higher in the CSF of patients with central nervous system infections compared to normal pressure hydrocephalus controls, suggesting the involvement of these factors in neuro-inflammation. CSF thrombin activity levels in the presence of known thrombin concentration were high in patients with central nervous system infections, and low in normal pressure hydrocephalus patients. Quantification of endogenous thrombin inhibitors protease nexin 1, amyloid precursor protein and anti-thrombin III in CSF by western blot indicated a significant elevation of amyloid precursor protein in infectious CSF. In conclusion, this study describes a novel and sensitive assay aimed at the detection of thrombin and aPC activity in CSF. This method may be useful for measuring these factors that reflect degenerative and protective influences of coagulation on neurological disorders. The study procedure was approved by the Ethics Committee of the Chaim Sheba Medical Center (approval No. 4245-17-SMC) on October 18, 2018.

A red-shifted Bioluminescence Resonance Energy Transfer (BRET) biosensing system for rapid measurement of plasmin activity in human plasma

Proteases are key signalling molecules for many physiological processes and their dysregulation is implicated in the progression of a range of diseases. Sensitive methods to measure protease activities in complex biological samples are critical for rapid disease diagnoses. The proteolytic activity of plasmin reflects the fibrinolysis state of blood and its deregulation can indicate pathologies such as bleeding events. While Bioluminescence Resonance Energy Transfer (BRET) is a powerful and sensitive method for the detection of protease activity, the commonly applied blue-shifted BRET² system, consisting of the Renilla luciferase Rluc2 and the large-stokes shift fluorescent protein GFP², suffers from light absorption and light scattering in human plasma samples. To address this challenge, we developed a red-shifted BRET-based plasmin sensor by substituting BRET² with the BRET⁶ system. BRET⁶ is composed of the red-shifted RLuc8.6 luciferase linked to the red light emitting fluorescent protein TurboFP635. The BRET⁶ biosensor exhibited 3-fold less light absorption in plasma samples compared to the BRET² sensor leading to an up to a 5-fold increase in sensitivity for plasmin detection in plasma. The limits of detection for plasmin were determined to be 11.90 nM in 7.5% (v/v) plasma with a 10 min assay which enables biologically relevant plasmin activities of thrombolytic therapies to be detected. While a colorigenic plasmin activity assay achieved a similar detection limit of 10.91 nM in 7.5% (v/v) human plasma, it required a 2 h incubation period. The BRET⁶ sensor described here is faster and more specific than the colorigenic assay as it did not respond to unspiked human plasma samples.

Thrombin-Induced Responses via Protease-Activated Receptor 1 Blocked by the Endothelium on Isolated Porcine Retinal Arterioles

PURPOSE

Thrombin, a serine protease, causes organ-specific responses to vessels. However, the mechanism by which thrombin affects the retinal microcirculation remains unclear. We examined the effects of thrombin on the retinal microvasculature and signaling mechanisms.

METHODS

Porcine retinal arterioles were isolated, cannulated, and pressurized (55 cmH₂O) without flow in this in vitro study. Videomicroscopy techniques recorded changes in diameter in the retinal arterioles in response to thrombin at concentrations ranging from 0.001 to 20 mU/ml.

RESULTS

Extraluminal administration of thrombin induced concentration-dependent vascular responses, that is, vasoconstriction at low concentrations less than 5 mU/ml and vasorelaxation with high concentrations greater than 5 mU/ml. However, intraluminal administration of thrombin (5 mU/m) did not constrict the retinal arterioles; in denuded vessels, intraluminal administration constricted the retinal arterioles. Thrombin-induced vasoconstriction was significantly (p < 0.01) suppressed by pretreatment with a protein kinase C (PKC) inhibitor and a protease-activated receptor (PAR)-1 inhibitor but not by PAR-2 and PAR-4 inhibitors or denudation. A rho kinase (ROCK) inhibitor also suppressed thrombin-induced vasoconstriction (5 mU/ml) compared with sodium nitroprusside. Endothelial denudation and pretreatment with an endothelial nitric oxide (NO) synthase inhibitor suppressed vasorelaxation caused by a high concentration of thrombin.

CONCLUSIONS

A low concentration of thrombin causes vasoconstriction of smooth muscles via PAR-1, PKC, and ROCK, and a high concentration of thrombin possibly causes vasorelaxation of the retinal arterioles via nitric oxide synthase activation in the endothelium. The vascular endothelium might block signaling of thrombin-induced vasoconstriction in the retinal arterioles when administered intraluminally.

Protein–polysaccharide complexes for enhanced protein delivery in hyaluronic acid templated calcium carbonate microparticles

Chimeric proteins facilitate protein–polysaccharide interactions for enhanced delivery and controlled release of proteins.

Intravitreal thrombin activity is elevated in retinal vein occlusion

To evaluate whether intravitreal thrombin activity is elevated in eyes with branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO) in comparison to healthy controls. Prospective clinical case series of 19 patients with BRVO, 13 patients suffering from CRVO and nine participants serving as controls. Vitreous taps were extracted from the central vitreous body, 200 μl frozen/thawed sample was immediately stabilized with 200 μl 5% human albumin, and 200 μl mixture thereof was stabilized with 200 μl 2.5 mol/l arginine, pH 8.6. Thrombin activity was determined chromogenically. Intravitreal levels of vascular endothelial growth factor (VEGF) as a marker for blood-retina barrier (BRB) breakdown were measured by a commercial chemiluminescent enzyme immuno assay (R&D). Intravitreal thrombin activity and VEGF levels were 1.6 ± 1.2 mIU/ml (mean value ± SD; range: 0.2-4.2 mIU/ml) and 554 ± 568 pg/ml (range: 20-2005 pg/ml) in BRVO-affected eyes, 2.6 ± 1.2 mIU/ml (range: 0.8-5.2 mIU/ml) and 1332 ± 1350 pg/ml (range: 58-3943 pg/ml) in eyes suffering from CRVO as well as 0.8 ± 0.8 mIU/ml (range: 0.2-2.7 mIU/ml) and 115 ± 120 pg/ml (range: 32-431 pg/ml) in controls. There are significant differences of intravitreal thrombin activity and intravitreal VEGF levels between eyes with BRVO, CRVO, and controls (P = 0.007 and P = 0.003, Kruskal-Wallis test). Intravitreal thrombin activity is significantly correlated with intravitreal VEGF levels (r = 0656; P < 0.001, Pearson correlation). Intravitreal thrombin activity might serve as a new marker for BRB breakdown or macular fibrin deposition in ophthalmology. Significant differences of intravitreal thrombin activity between eyes with BRVO, CRVO, and healthy controls might offer new therapeutic strategies for RVO-affected eyes. The effect of oral and intravitrealy injected direct thrombin inhibitors needs to be evaluated in further investigations.

Comparing techniques: the use of recalcified plasma in comparison with citrated plasma alone and in combination with thrombin in ultrastructural studies

Fibrin plays a vital role in the coagulation process and fibrin fiber morphology can be studied using ultrastructural techniques. When studying the ultrastructure of fibrin networks, thrombin may be added to the plasma, ensuing fibrin network formation. The question that arises is whether there are differences in morphology when thrombin is added to plasma, versus morphology observed when plasma from citrated or recalcified citrated whole blood, is studied. The current study therefore aimed to compare ultrastructure of platelets and fibrin networks from these three techniques. Results indicated comparable platelet ultrastructure between smears formed from the plasma of citrated blood and that of the citrated recalcified blood. This method might give us further information regarding the 'natural state' fibrin assembly and association with platelets, when studying haemostasis. However, when studying the ultrastructure of fibrin networks, the addition of thrombin is necessary to form an expansive, fully coagulated layer of fibrin fibers.

Bi-cell surface plasmon resonance detection of aptamer mediated thrombin capture in serum

The serine protease coagulation factor thrombin functions primarily in hemostasis, but is also involved in atherosclerosis, thromboembolic disease, cancer and inflammatory disease. Direct measurement of coagulation proteins including thrombin in plasma samples poses a significant challenge because of lack of specific probes and low thrombin concentrations. In addition, high plasma protein concentrations in samples can result in high backgrounds. These challenges were overcome using a bi-cell surface plasmon resonance (SPR) spectrometer with an immobilized thrombin aptamer to measure thrombin in samples passed through a low volume flow cell. For thrombin in Tris-EDTA buffer, the limit of detection (LOD) was 25 nM. Coefficient of variation (CV) for detection of 50 nM was 12.2% and 12.4% for intra and inter-day measurements respectively. This detection was specific for both thrombin aptamer and for thrombin. Using serum samples spiked with thrombin, the LOD was 50 nM with a linear range of detection from 50 nM to 200 nM. However use of serum samples was associated with consistent, low-level background drift. The contributions of nonspecific protein absorption onto the sensor surface and sample flow speed were assessed, and strategies to reduce this background drift were explored. We conclude that the bi-cell SPR platform with an aptamer capture probe can be employed as a highly sensitive real-time, label-free biosensor for the detection of coagulation factors in plasma samples.

Thromboelastometry in patients with severe sepsis and disseminated intravascular coagulation

Severe sepsis induces coagulopathy, which may lead to disseminated intravascular coagulation (DIC). Thromboelastometry is a point-of-care whole blood coagulation monitor, which has been validated in human endotoxemia model. We assessed thromboelastometry in severe sepsis and overt DIC and investigated its applicability in differentiating sepsis-related coagulation disturbances. Thromboelastometry (EXTEM and FIBTEM tests) and traditional coagulation assays were analyzed in 28 patients with severe sepsis, 12 of who fulfilled the criteria of overt DIC on admission. Ten healthy persons served as controls. Coagulation parameters, clotting time, clot formation time (CFT), alpha angle, maximal clot firmness (MCF) and lysis index at 60 min, were registered. In patients with overt DIC, EXTEM MCF, CFT and alpha angle differed from that in both healthy controls and patients without DIC, indicating hypocoagulation (MCF 52, 63 and 68 mm; CFT 184, 88 and 73 s; and alpha angle 58, 72 and 76 degrees , respectively, P < 0.01 for all). In patients without DIC, the trend was toward hypercoagulation in EXTEM and FIBTEM MCF (68 vs. 63 mm, P = 0.042 and 23 vs. 15 mm, P = 0.034, respectively). Receiver operating characteristic curves showed that MCF, CFT and alpha angle discriminated patients with overt DIC moderately (area under curve 0.891, 0.815 and 0.828, respectively, P < 0.001 for all). Traditional coagulation assays showed progressively worsening coagulopathy from controls to septic patients without DIC and further to those with overt DIC. We conclude that thromboelastometry may be a valuable tool in assessing whole blood coagulation capacity in patients with severe sepsis with and without overt DIC.

The Extrinsic Coagulation Activity Assay

A chromogenic assay for the tissue factor—mediated thrombin generation was developed, the extrinsic coagulation activity assay: 50 µL citrated plasma is incubated with 5 µL tissue factor in 6% albumin and 250 mM CaCl2. After 1-minute (37°C) coagulation reaction time, (extrinsic coagulation activity assay with 1-minute coagulation reaction time; generating normally about 1 IU/mL thrombin) 100 µL 2.5 M arginine is added to stop hemostasis activation. Generated thrombin is then chromogenically quantified. The normal extrinsic coagulation activity assay range is 100% ± 20%. Extrinsic coagulation activity assay in plasma of patients on heparin or coumarines is about 10-fold lower. Advantages of extrinsic coagulation activity assay: normal range of extrinsic hemostasis is truly represented, patients prone to hyper-activated extrinsic pathway are detected, anticoagulants result in respective test inhibition, fibrinogen/fibrin concentration does not artefactually alters the test result, plasma matrix is not changed significantly in the assay, and assay results are IU/mL thrombin or % of normal, which can be measured by every normal photometer.

Kallikrein activates prothrombin

Kallikrein is a multitalented enzyme in hemostasis and inflammation. Normally, kallikrein is formed in intrinsic hemostasis and activates factor XII. A total of 10 microL of 0 to 100 microg/mL human plasma kallikrein in 6% human albumin-PBS were incubated with 90 microL 111.1 microg/mL prothrombin in 6% human albumin in absence and presence of 23 mM Ca(++). After 0 to 64 minutes (37 degrees C), 100 microL of 2.5 M arginine, pH 9, were added. Fifty microliters of 0.72 mM HD-CHG-Ala-Arg-pNA in 1.36 M arginine were added and increase in absorbance at 405 nm was determined. Within 8 minutes (37 degrees C), 1 microg/mL kallikrein, ie, 2.5% of the normal plasmatic prekallikrein concentration, generates approximately 3 mIU/mL thrombin in absence and 27 mIU/mL thrombin in presence of Ca(++). Kallikrein can directly activate prothrombin; there is a shortcut in the intrinsic hemostasis system that generates catalytic amounts of thrombin without following the known intrinsic clotting pathway.

The Recalcified Coagulation Activity

Thrombin activity generated after plasma recalcification is of analytical and clinical interest. Fifty microliters of citrated plasma was recalcified with 5 µL of 250 mM CaCl2. After 0 to 90 minutes (37°C) 50 µl 2.5 M arginine, pH 8.6, was added. After 20 minutes, thrombin was chromogenically quantified. In normal recalcified plasma, the generated thrombin activity is about 0.1-0.2 IU/ml (37°C) when fibrin generation starts. Pooling of normal plasmas increases the generated thrombin activity about 3-fold. Plasmas of patients on heparin or coumarin generate about 10-fold less thrombin activity. Freezing of pooled plasma at −20°C and thawing at room temperature or 37°C increases thrombin generation approximately 1.5- or 2-fold, respectively. Only thrombin activities in the ascending part of the thrombin generation curve (RECA-t2/RECAt1>1) are valid. So a prothrombotic state in blood or plasma can be diagnosed.

Analysis of hemostasis alterations in sepsis

This laboratory study tested new methods to analyze hemostasis alterations in septic patients. Samples of ethylenediamine tetraacetic acid (EDTA) plasma and citrated plasma were collected from 62 patients with clinical diagnosis of sepsis. Additionally, a subset of EDTA-plasma samples from each patient was stabilized 1 + 1 with 2.5 mol/l arginine, pH 8.6, to conserve the real hemostasis activation state. EDTA-arginine plasma, EDTA plasma and citrated plasma samples were tested in duplicate. The patients at admission to the intensive care unit had 36 +/- 26 (normal, 0.8 +/- 0.2) ng/ml global endotoxin reactivity, 188 +/- 66% (normal, 100 +/- 20%) fibrinogen function, 179 +/- 66% (normal, 100 +/- 20%) fibrinogen antigen, 4.0 +/- 3.6 (normal, 0.049 +/- 0.025) microg/ml D-dimer, 313 +/- 307% (normal, 100 +/- 30%) plasmin-antiplasmin complex, 8.7 +/- 11.4 (normal, 1.1 +/- 0.7) U/ml plasminogen activator inhibitor-1, 12.1 +/- 10.5 (normal, 1.3 +/- 0.4) ng/ml thrombin-antithrombin III complex, 173 +/- 62% (normal, 100 +/- 20%) thrombin, 568 +/- 225 (normal, 140 +/- 42) pg/ml tissue factor, and 2.56 +/- 2.48 (normal, 0.19 +/- 0.04) microg/ml soluble intercellular adhesion molecule-1. Endotoxin (lipopolysaccharide and/or beta-glucan) reactivity (EDTA plasma), fibrinogen function + antigen + ratio and plasminogen activator inhibitor-1 (citrated plasma), and D-dimer, soluble intercellular adhesion molecule-1, thrombin activity (EDTA-arginine-stabilized plasma) presented large aberrations in septic patients when compared with normal values and may therefore be particularly interesting as markers of hemostasis alteration. Whether the observed alterations are of clinical significance has to be determined in well defined patient groups.

The efficiency of anti-activated factor X and anti-activated factor II anticoagulants

Six thrombin-generation inhibitors or thrombin inhibitors were compared in the extrinsic coagulation activity assay (EXCA), where the normal thrombin generation is about 1 IU/ml within 1 min (37 degrees C). Unfrozen pooled normal citrated plasma was supplemented on flat-bottom wells (23 degrees C) with increasing concentrations of dalteparin, danaparoid, heparin, fondaparinux, hirudin, or argatroban. To 50 microl plasma, 5 microl of 1.5 ng/ml tissue factor, 6% bovine serum albumin, and 250 mmol/l CaCl2 were added. After 1 and 2 min coagulation reaction time at 37 degrees C (EXCA-1 and EXCA-2), 100 microl of 2.5 mol/l arginine and 0.16% Triton X 100, pH 8.6, were added. After 3 min (23 degrees C), 25 microl of 1 mmol/l CHG-Ala-Arg-pNA in 1.25 mol/l arginine, pH 8.7, were added, and the linear increase in absorbance with time was determined at 405 nm. The 50% inhibitory concentrations of plasmatic anticoagulants tested in the EXCA-1 (37 degrees C) were 0.025 IU/ml dalteparin, 0.13 U/ml danaparoid, 0.12 IU/ml heparin, 1.3 microg/ml fondaparinux, 2.4 ng/ml hirudin, and 1 microg/ml argatroban. From the 50% inhibitory concentration of hirudin it can be concluded that inhibition of about 30 mIU/ml thrombin halves the normal EXCA-1 value (i.e. if about 0.1 IU/ml thrombin are inactivated, then thrombin cannot self-amplify its generation 10-fold). The efficiency of any clinically used plasmatic anticoagulant can be monitored in the EXCA.

Thrombin generation by hemolysis

Hemolysis is the fragmentation of erythrocytes into microparticles (Hb-MP). Clinical hemolysis can result in a severe procoagulant state. The influence of Hb-MP on thrombin generation was quantified. Unfrozen citrated normal plasma (five donors) was supplemented with 0 or 1 g/l Hb-MP obtained through erythrocyte destruction by hypotonic lysis, freezing/thawing, or blood oxidation with 1 or 2 mmol/l chloramine-T. Pooled normal plasma was supplemented with 0-10 g/l Hb-MP and with 0-1 IU/ml low-molecular-weight heparin (dalteparin). Samples (50 microl) were tested in the recalcified coagulation activity assay. At 10 min coagulation reaction time the hypotonic lysis of erythrocytes appears to be the most procoagulant condition, followed by twice freezing/thawing, three times freezing/thawing, and once freezing/thawing. Oxidation of whole blood with 1 or 2 mmol/l chloramine-T decreases thrombin generation by about 20 or 50%, respectively. The thrombin generation in 1 mmol/l chloramine-T or 2 mmol/l oxidized plasma decreases by about 70 or 85%, respectively. The 50% inhibitory concentrations of low-molecular-weight heparin against recalcified thrombin generation are 0.01, 0.025, or 0.035 IU/ml for plasma supplemented with 0, 0.1, or 1 g/l Hb-MP, respectively. The recalcified coagulation activity assay allows one to quantify thrombin generation in critical hemolytic samples. It is suggested to find the appropriate pharmacologic dose of low-molecular-weight heparin.

Influence of coagulation factors on extrinsic thrombin generation

The extrinsic coagulation activity assay (EXCA) is a new thrombin generation test for the tissue factor pathway of coagulation. The EXCA was performed with 10 parts citrated plasma of different contents of fibrinogen. One part tissue factor, 250 mmol/l CaCl(2), generating about 1 IU/ml thrombin within 1 min (37 degrees C). After 0-30 min 2.5 mol/l arginine (pH 8.6) Generated thrombin was detected by addition of CHG-Ala-Arg-pNA and measurement of triangle upA/t. The EXCA is dependent on factors 10% of the factor VII norm in the sample achieves 70-80% of the thrombin generation norm. The EXCA is not dependent on factors VIII, IX, XI and XII. Even in antithrombin III-deficient plasma, a phase of thrombin inhibition appears after the thrombin peak. Supplemented purified fibrinogen resulted in decreased thrombin generation in the important. Fibrinogen seems to act as antithrombin I; thrombin might be entrapped in the nascent fibrin. The EXCA is suitable to diagnose the level of extrinsic factors in patient plasma.

Influence of coagulation factors on intrinsic thrombin generation

The intrinsic coagulation activity assay (INCA) is a new thrombin-generation test that imitates the intrinsic pathway of blood coagulation. The aim of the present study was to investigate the influence of the main coagulation factors on the INCA. The INCA was performed with citrated plasma samples supplemented with different amounts of fibrinogen. The INCA and activated partial thromboplastin time determination were performed with factor-depleted plasmas and with mixtures of depleted plasmas with normal plasma. Supplemented purified fibrinogen resulted in a decrease of intrinsic thrombin generation (50% inhibitory concentration = 0.8 g/l). The INCA depends on the intrinsic factors (factors VIII, IX, XI and XII) and on the factors of the common pathway (factors II, V and X): for normal thrombin generation, at least about 50% of normal factor II is necessary. For the majority of factors, the sensitivity of the INCA appears to be approximately one order of magnitude better than that of the activated partial thromboplastin time. The INCA allows one to diagnose defects in the intrinsic coagulation system and might be a useful test to support development and characterization of new drugs targeted at the intrinsic generation of thrombin.