FV Activity Research Articles

Inhibition of thrombin‐mediated factor V activation contributes to the anticoagulant activity of fibrinogen γ′

Besides its role in blood clotting, fibrinogen exerts a poorly understood anticoagulant function by binding thrombin and modulating its activity. In particular, the γA/γ' fibrinogen isoform binds with high affinity to thrombin exosite II through the anionic carboxyl-terminal end of the γ' chain. This interaction down-regulates thrombin-mediated factor VIII (FVIII) activation, but its effect on FV activation is unknown. To investigate the overall anticoagulant activity of fibrinogen and particularly of fibrinogen γ' in plasma, and to verify whether the fibrinogen γ' carboxyl-terminal peptide affects thrombin-mediated FV activation. Thrombin generation was measured by calibrated automated thrombography in whole and defibrinated plasma and in plasma supplemented with the (sulfated) fibrinogen γ' carboxyl-terminal peptide (0-500μmol L(-1) ). The effect of the peptide on thrombin-mediated FV activation was studied in model systems and in plasma. Total fibrinogen prolonged the lag time of thrombin generation at low tissue factor (TF) concentrations. The fibrinogen γ' peptide dose-dependently prolonged the lag time and decreased the peak height of thrombin generation at low TF, whereas a scrambled control peptide was ineffective. These effects persisted in the presence of an anti-FVIII antibody, suggesting that the peptide may also inhibit thrombin-mediated activation of FV. This was confirmed in model systems and in plasma. Total fibrinogen and the fibrinogen γ' peptide have an overall anticoagulant effect on thrombin generation determined at low TF. Inhibition of thrombin-mediated FV activation by the fibrinogen γ' peptide is a novel mechanism of the anticoagulant activity of fibrinogen γ'.

Combined effects of fibrinogen genetic variability on atherosclerosis in patients with or without stable angina pectoris: Focus on the coagulation cascade and endothelial function

BackgroundFibrinogen is a coagulation/inflammatory biomarker strongly associated with atherogenesis. Data have reported that the genetic variability on fibrinogen chains may affect the atherosclerotic process and the risk of coronary artery disease (CAD). We examined the combined effects of the G455A and the G58A fibrinogen genetic polymorphisms on prothrombotic profile, endothelial function and the risk of CAD in a Caucasian population. MethodsWe recruited 422 patients with angiographically documented CAD and 277 controls matched for age and gender. The two polymorphisms were genotyped by polymerase chain reaction and restriction endonuclease digestion. Fibrinogen and D-Dimers levels, as well as factors' (f) V, X activity were measured by standard coagulometry techniques. Endothelial function was assessed by the flow mediated dilatation (FMD) of the brachial artery. ResultsThe two polymorphisms had no significant effect on the risk for CAD. Although the 58AA subjects had not significantly different levels of fibrinogen compared with the 58GG+GA in both groups (p=NS), we importantly found that the 455AA homozygosity was associated with increased fibrinogen levels not only in the control group (p=0.035), but also in the CAD group (p<0.001) compared to the G allele carriers. Moreover, both the 58AA (p=0.016) and 455AA homozygotes (p=0.022) presented with higher levels of D-Dimers in the CAD group. Interestingly, the 455AA homozygotes had increased fV activity in the CAD group (p=0.048). However, no significant effects were observed on fX activity and FMD. ConclusionsBoth fibrinogen polymorphisms are capable to modify the atherosclerotic process via their effects on the coagulation cascade.

Factor Xa Activation of Factor V Is of Paramount Importance in Initiating the Coagulation System

Background— Generation of active procoagulant cofactor factor Va (FVa) and its subsequent association with the enzyme activated factor X (FXa) to form the prothrombinase complex is a pivotal initial event in blood coagulation and has been the subject of investigative effort, speculation, and controversy. The current paradigm assumes that FV activation is initiated by limited proteolysis by traces of (meizo) thrombin. Methods and Results— Recombinant tick salivary protein TIX-5 was produced and anticoagulant properties were studied with the use of plasma, whole blood, and purified systems. Here, we report that TIX-5 specifically inhibits FXa-mediated FV activation involving the B domain of FV and show that FXa activation of FV is pivotal for plasma and blood clotting. Accordingly, tick feeding is impaired on TIX-5 immune rabbits, displaying the in vivo importance of TIX-5. Conclusions— Our data elucidate a unique molecular mechanism by which ticks inhibit the host’s coagulation system. From our data, we propose a revised blood coagulation scheme in which direct FXa-mediated FV activation occurs in the initiation phase during which thrombin-mediated FV activation is restrained by fibrinogen and inhibitors.

Quality of frozen transfusable plasma prepared from whole blood donations in Canada: An update

Transfusable plasma is obtained by processing whole blood donations, by apheresis, or as solvent/detergent plasma (SD plasma), a pooled pathogen-reduced plasma product. The quality of plasma is typically assessed by testing the activities of multiple coagulation-related plasma proteins, due to a lack of clinical trial data linking plasma composition to clinical endpoints. We sought to update previous quality surveys of Canadian frozen plasma (FP; manufactured from single donor whole blood donation and frozen within 24h of phlebotomy), to provide transfusionists with a more complete picture of its characteristics. FP units (n=131) were tested for: the activity of factors V, VII, VIII, X, and XI, protein S (PS), α2-antiplasmin (AP), and fibrinogen; and the activated partial thromboplastin (APTT) and prothrombin (PT) times. Comparisons were made to: previous Canadian FP surveys; and to studies of single-donor plasma and SD plasma from other nations. Mean FVIII, fibrinogen, or APTT values did not differ from the previous annual survey of Canadian FP; FV activity was increased and PT values decreased. FP produced with or without leukoreduction differed only in mean APTT. Canadian FP exhibited generally similar quality to that reported by other organizations in Europe and Asia for similarly manufactured single-donor plasma, but contained notably higher PS and AP (≈ four-fold) activities than did SD plasma. Our results indicate that Canadian FP is of similar quality to single-donor products produced in other jurisdictions. While it is of arguably superior in vitro quality to an SD plasma product recently licensed in Canada, these differences are highly unlikely to have clinical significance for most indications for plasma transfusion.

Prothrombotic gene variants as risk factors of acute myocardial infarction in young women

BackgroundAcute myocardial infarction (AMI) in young women represent an extreme phenotype associated with a higher mortality compared with similarly aged men. Prothrombotic gene variants could play a role as risk factors for AMI at young age.MethodsWe studied Factor V Leiden, FII G20210A, MTHFR C677T and beta-fibrinogen -455G>A variants by real-time PCR in 955 young AMI (362 females) and in 698 AMI (245 females) patients. The data were compared to those obtained in 909 unrelated subjects (458 females) from the general population of the same geographical area (southern Italy).ResultsIn young AMI females, the allelic frequency of either FV Leiden and of FII G20210A was significantly higher versus the general population (O.R.: 3.67 for FV Leiden and O.R.: 3.84 for FII G20210A; p<0.001). Among AMI patients we showed only in males that the allelic frequency of the MTHFR C677T variant was significantly higher as compared to the general population. Such difference was due to a significantly higher frequency in AMI males of the MTHFR C677T variant homozygous genotype (O.R. 3.05).Discussion and conclusionOur data confirm that young AMI in females is a peculiar phenotype with specific risk factors as the increased plasma procoagulant activity of FV and FII. On the contrary, the homozygous state for the 677T MTHFR variant may cause increased levels of homocysteine and/or an altered folate status and thus an increased risk for AMI, particularly in males. The knowledge of such risk factors (that may be easily identified by molecular analysis) may help to improve prevention strategies for acute coronary diseases in specific risk-group subjects.

Effects of extraction condition on structural features and anticoagulant activity of F. vesca L. conjugates

From the air-dried Wild strawberry (Fragaria vesca L., family Rosaceae) leaves five water-soluble glycoconjugates Fv I–V by different extraction conditions have been isolated. Effects of extraction steps/agents on chemical composition and anticoagulant activity of Fv I–V were examined. Dark brown F. vesca conjugates Fv I–V were recovered in 4.5–8.4% yields, based on dry herb. Isolates were composed of carbohydrate, phenolic and protein components. Fv I–V displayed on HPLC broad molecule-mass distribution patterns with dominance of low molecule-masses 9–14kDa. Their carbohydrate parts revealed high hexuronic acids content (35–60%) while the dominant neutral sugars – galactose, arabinose and rhamnose were found in lower amounts and indicated the presence of rhamnogalacturonans associated with arabinogalactans in all F. vesca preparations. In all Fv I–V isolates high polyphenolic contents were determined, whereas proteins were found in low amounts only. In in vitro experiments on human pooled plasma Fv I–V showed at higher concentrations complete inhibition of plasma clot formation and the most active conjugates in aPTT, PT and TT tests were shown to be Fv I and Fv III, containing the highest amounts of phenolics.

Analysis of prolonged storage on coagulation Factor (F)V, FVII, and FVIII in thawed plasma: is it time to extend the expiration date beyond 5 days?

According to AABB standards, fresh-frozen plasma (FFP) should be thawed at 30 to 37°C and expire after 24 hours. An increase in the aggressive management of trauma patients with thawed plasma has heightened the risk of plasma waste. One way to reduce plasma waste is to extend its shelf life, given that the full range of therapeutic efficacy is maintained. We evaluated the effect of prolonged storage at 1 to 6°C on the activity of Factor (F)V, FVII, and FVIII in plasma thawed at 37 or 45°C. Group O plasma from healthy donors (n=20) was divided into 10 pairs and frozen and stored at not more than -18°C. One sample from each pair was thawed at 37 or 45°C, and all were stored at 1 to 6°C. Samples were analyzed for FV, FVII, and FVIII activity on Days 0, 5, 10, 15, and 20. Plasma thawing time was 17% less at 45°C than at 37°C. No differences were observed between thawing groups in coagulation activity of FV, FVII, and FVIII during the 20-day storage period (p>0.12). In both groups, the activity of FV and FVIII decreased over time but remained within a normal range at 10 days. Although levels of plasma clotting factors are reduced in storage, therapeutic levels of FV and FVIII are maintained in thawed plasma stored for up to 10 days at 1 to 6°C. Thawing of FFP at 45°C decreases thawing time but does not affect the activity of FV, FVII, and FVIII.

Genetic modulation of the FVLeiden/normal FV ratio and risk of venous thrombosis in factor V Leiden heterozygotes

The factor (F)V Leiden mutation causes activated protein C (APC) resistance by decreasing the susceptibility of FVa to APC-mediated inactivation and by impairing the APC-cofactor activity of FV in FVIIIa inactivation. However, APC resistance and the risk of venous thromboembolism (VTE) vary widely among FV Leiden heterozygotes. Common F5 genetic variation probably contributes to this variability. APC resistance was determined in 250 FV Leiden heterozygotes and 133 normal relatives using the prothrombinase-based assay, which specifically measures the susceptibility of plasma FVa to APC. The effects of 12 F5 single-nucleotide polymorphisms (SNPs) on the normalized APC sensitivity ratio (nAPCsr) and on FV levels were determined by multiple regression analysis. In FV Leiden heterozygotes,VTE risk increased with increasing nAPCsr, reaching an odds ratio (OR) of 9.9 (95% confidence interval [CI] 1.2–80.5) in the highest nAPCsr quartile. The minor alleles of several F5 SNPs, including 327 A/G (Q51Q), 409 G/C (D79H), 2663 A/G(K830R, T2 haplotype), 6533 T/C (M2120T) and 6755 A/G (D2194G, R2 haplotype), increased the nAPCsr in FV Leiden heterozygotes, but not in their normal relatives. Most of these effects could be attributed to a shift in the FV(Leiden)/normal FV ratio. Four FV Leiden heterozygotes with extremely high nAPCsr turned out to be pseudo-homozygotes, i.e. they carried a deleterious mutation on the non-Leiden allele. In FV Leiden heterozygotes, the prothrombinase-based nAPCsr is a marker of VTE risk and is modulated by common F5 SNPs that affect the FV(Leiden)/normal FV ratio in plasma.

Evidence for a Factor IX-Independent Role for Factor XI in Thrombin Generation

Abstract 2244In the widely used activated partial thromboplastin time (aPTT) assay, fibrin formation is induced by a series of sequential activations of the plasma protease zymogens factor (f) XII, fXI, fIX, fX and prothrombin, in that order. Conversion of prothrombin to the protease α-thrombin results in fibrin formation. α-Thrombin also enhances its own generation through activation of the cofactors fV and fVIII. While the linear sequence of reactions in the aPTT implies that loss of any single protease should have a comparable deleterious effect on the system, it is recognized that complete deficiency of a protein near the start of the sequence (e.g. fXII or fXI) results in greater aPTT prolongation than deficiency of proteins further down the sequence (e.g. fIX). This implies that proteases activated early in the process have multiple plasma substrates. For example, fXIa was recently reported to activate fVIII and fV (JTH 8;1532:2010), in addition to its role in fIX activation. Here, we present evidence that fXIa contributes to α-thrombin generation in the absence of fIX through activation of fX and/or fV.We noted that an anti-fXI antibody (O1A6) prolonged the aPTT of plasma from a patient with severe hemophilia B (fIX antigen undetectable) or plasma immunodepleted of fIX. This observation held even when an anti-fIX antibody was added to neutralize potential traces of fIX. Addition of activated fXI (fXIa - 3 nM) directly to fIX-deficient recalcified plasmas induced clot formation, and the time to clot formation was prolonged by O1A6. To further exclude the possibility that traces of fIX were contributing to thrombin generation, we confirmed the results using plasma from mice with combined complete deficiencies of fXII, fXI, and fIX. We tested the capacity of fXIa to cleave/activate fX and fV, the protease zymogen and cofactor, respectively, immediately downstream of fIX in the coagulation cascade. FX, the zymogen of the protease fXa, is evolutionarily related to fIX. SDS-PAGE analysis confirmed that fXIa cleaves fX. FX cleaved by fXIa demonstrated fXa activity in a chromogenic substrate assay, and converted prothrombin to α-thrombin in the presence of fVa and phospholipid. As previously reported, fXIa readily cleaved fV. The cleavage pattern differed from that generated by α-thrombin, however, formation of the fVa light chain was clearly evident. In a plasma clotting assay designed to measure either fXa or fVa activity, fX or fV pre-incubated with fXIa significantly shortened the clotting time of fIX-deficient plasma, while fX or fV pre-incubated with vehicle did not.In thrombin generation assays, fXIa (1.25 to 15 nM) induced thrombin generation in fIX-deficient plasma supplemented with anti-fIX antibody in a concentration dependent manner. FXIa did not induce thrombin generation in plasma lacking fV, or in fIX-deficient plasma containing the fXa inhibitor apixaban. This indicates that fXIa is working at the level of fX/fV in this assay, and is not directly converting prothrombin to α-thrombin. A recombinant variant of fXIa lacking the major fIX-binding exosite (fXIaPKA3, J Biol Chem 1996;271:29023) demonstrated a marked defect, compared to wild type fXIa (fXIaWT), in its capacity to induce thrombin generation in normal plasma. However, in fIX-deficient plasma, fXIaPKA3 and fXIaWT are comparable in their ability to enhance thrombin generation, supporting the premise that fXIa is acting through activation of fX and/or fV in the absence of fIX.Previously, we observed that fXI deficient mice and fIX deficient mice are comparably resistant to carotid artery thrombosis induced by exposure of the vessel to ferric chloride, despite having very different propensities to bleed. The animals were uniformly resistant to thrombosis with 5% FeCl3, and some were resistant at 7.5% FeCl3. All experienced vessel occlusion with 10% FeCl3. This is consistent with fXIa contributing to thrombosis in this model through fIX activation. However, we observed that some mice with combined fIX and fXI deficiency were resistant to FeCl3 concentrations up to 12.5%, implying that fXIa was contributing to thrombosis in a fIX-independent manner, as well. These results are consistent with those from the in vitro assays described above, and support the hypothesis that fXIa contributes to thrombin generation through fIX-dependent and fIX-independent processes. Disclosures:Tucker:Aronora, LLC: Employment, Equity Ownership. Gruber:Aronora, LLC: Consultancy, Equity Ownership.

Modulating the Factor V Procofactor to Cofactor Transition Using Recombinant B-Domain Fragments

Abstract 376Activation of clotting factors from their inactive precursor states by limited and discrete proteolysis is a hallmark of coagulation. Prothrombinase, the physiological activator of prothrombin, is comprised of the serine protease factor Xa (FXa) and its cofactor factor Va (FVa). The precursor of FVa, FV, is an inactive procofactor and cannot participate to any significant degree in prothrombinase. It is well established that the large central B domain of FV (domain organization of A1-A2-B-A3-C1-C2) stabilizes the inactive procofactor state, however the mechanism by which this occurs is poorly defined. Since FVa has such a profound impact on thrombin generation and clot formation, defining the mechanism by which FV is kept inactive may reveal a unique way to target the cofactor for therapeutic gain. We previously demonstrated that deletion of a conserved region of the B domain enriched in basic residues converts FV to an active cofactor (JBC 2007, 282: 15033). Here we provide new insights into the mechanism by which the basic region of the B-domain contributes to maintaining FV as an inactive procofactor. Using a bacterial expression system, we generated FV B-domain fragments and assessed their ability to disrupt the procofactor to cofactor transition. The FV variant FV-810 (residues 811–1491 deleted), which lacks over 80% of the B-domain including the basic region, possesses activity comparable to FVa in clotting assays, thrombin generation assays, and in vitro prothrombin activation reactions. Addition of a FV B-domain fragment containing the basic region (residues 951–1008; ‘basic peptide’) inhibited FV-810 activity in all three assays. As a control, no inhibitory effect was observed with a non-homologous peptide from the FVIII B-domain. Surprisingly, the basic peptide did not inhibit FVa in these assays, nor did it inhibit FV-810 or other FV variants that had been pre-incubated with thrombin. These results indicate that additional B-domain sequences present in FV-810 must somehow contribute to the inhibitory effect of the basic region. Analysis of the B-domain sequences within FV-810 and other cofactor-like FV variants revealed a concentration of acidic residues between Thr1492 and Asn1538 that may help to stabilize FV in an inactive state most likely through an electrostatic interaction with the basic region. In support of this model, FV BR152, a variant that possesses the basic region but lacks the acidic region, has FVa-like activity in clotting assays and prothrombin activation assays. Unlike the basic peptide, a peptide derived from the acidic region (residues 1492–1538) did not inhibit the activity of FV BR152, indicating that the acidic region must be located proximal to the A3 domain in order to inhibit FV. To further probe the mechanism by which the basic peptide functions, we directly monitored FXa binding to FV-810 on phospholipid vesicles using fluorescence anisotropy. In the absence of the basic peptide, labeled FXa bound to membrane-bound FV-810 with a Kd of ∼1 nM in a 1:1 stoichiometry. Addition of the FV basic peptide significantly reduced FXa binding to FV-810 in a dose-dependent manner, indicating competition between FXa and the basic peptide for FV-810. Consistent with the results of the functional assays, the basic peptide had no effect on FXa binding to membrane-bound FVa. Taken together our data support a model in which the basic B-domain region of FV inhibits the cofactor activity of FV through a functional interaction with an acidic region proximal to the A3 domain, thereby masking a FXa binding site that is exposed following thrombin cleavage of FV at Arg1545. These findings offer important new insights into how FV is kept as an inactive procofactor and provide key mechanistic clues into how the B-domain participates in this process. Moreover, these results demonstrate a novel strategy to regulate FV cofactor activity by using functional elements of the B-domain to shift an active cofactor back to an inactive procofactor. Disclosures:No relevant conflicts of interest to declare.

Haemostatic abnormalities in cats with naturally occurring liver diseases

Alterations in the haemostatic system were characterized in cats with different naturally occurring liver diseases. The study looked at 44 healthy cats and 45 cats with different liver diseases confirmed histologically or cytologically (neoplasia, n=9; inflammation, n=12; hepatic lipidosis, n=13; other degenerative liver diseases, n=11). The following parameters were evaluated: platelet count; prothrombin time; activated partial thromboplastin time; thrombin time; factor (F) II, FV, FVII, FX, and FXIII activities; fibrinogen concentration; activities of antithrombin, protein C, plasminogen, and α(2)-plasmin inhibitor, and D-dimer concentration. In cats with liver diseases, 44/45 (98%) had one or more abnormalities of the coagulation parameters measured. In cats with inflammatory liver diseases, increased D-dimer concentrations and decreased FXIII activity were the most consistent abnormalities and were found in 83% and 75% of cats, respectively. The most common abnormality in cats with neoplastic liver disease was FXIII deficiency (78%). The most consistent abnormalities in cats with hepatic lipidosis were increased FV activity and D-dimer concentration with 54% of cats having values above the reference range for both parameters. Cats with miscellaneous degenerative liver disease most frequently showed FXIII deficiency (64%). The results of this study show that alterations of single haemostatic components are a frequent finding in cats with liver disease. Activation of haemostasis with subsequent consumptive coagulopathy (rather than decreased synthesis) seems to be responsible for these alterations. Increased blood levels of different haemostatic components in cats with inflammatory lesions may be related to an acute phase reaction.

Development of a microplate coagulation assay for Factor V in human plasma

BackgroundFactor V (FV) in its activated form, FVa, is a critical regulator of thrombin generation during fibrin clot formation. There is a need of a simple, fast, and inexpensive microplate-based coagulation assay to measure the functional activity of FV in human plasma. The objective of this study was to develop a microplate-based assay that measures FV coagulation activity during clot formation in human plasma, which is currently not available.MethodsThe FV assay requires a kinetic microplate reader to measure the change in absorbance at 405nm during fibrin formation in human plasma. The FV assay accurately measures the time, initial rate, and extent of fibrin clot formation in human plasma.ResultsThe FV microplate assay is simple, fast, economical, sensitive to approx 24-80pM, and multiple samples may be analyzed simultaneously. All the required materials are commercially available. Standard curves of time or initial rate of fibrin clot formation vs FV activity in the 1-stage assay (Without activation by thrombin) may be used to measure FV activity in samples of human plasma. The assay was used to demonstrate that in nine patients with disseminated intravascular coagulation (DIC), the FV 1-stage, 2-stage (With activation by thrombin), and total (2-stage activity - 1-stage activity) activities were decreased, on average, by approximately 54%, 44%, and 42%, respectively, from prolonged clot times when compared to normal pooled human reference plasma (NHP). The results indicate that the FV in the DIC patient plasmas supported both a delayed and slower rate of fibrin clot formation compared with NHP; however, the extent of fibrin clot formation in the DIC patients remained largely unchanged from that observed with NHP.ConclusionsThe FV microplate assay may be easily adapted to measure the activity of any coagulation factor using the appropriate factor-deficient plasma and clot initiating reagent. The microplate assay will find use in both research and clinical laboratories to provide measurement of the functional coagulation activity of FV in human plasma.

Homozygous F5 deep‐intronic splicing mutation resulting in severe factor V deficiency and undetectable thrombin generation in platelet‐rich plasma

Coagulation factor (F) V deficiency is associated with a bleeding tendency of variable severity, but phenotype determinants are largely unknown. Recently, we have shown that three patients with undetectable plasma FV and mild bleeding symptoms had sufficient residual platelet FV to support thrombin generation in platelet-rich plasma (PRP). Therefore, we hypothesized that FV-deficient patients with severe bleeding manifestations may lack platelet FV. To characterize a FV-deficient patient with a severe bleeding diathesis. We performed FV mutation screening and functional studies in a 31-year-old male (FV:C < 1%) with umbilical bleeding at birth, recurrent hemarthrosis and muscle hematomas, and a recent intracranial hemorrhage. The proband was homozygous for a deep-intronic mutation (F5 IVS8 +268A→G) causing the inclusion of a pseudo-exon with an in-frame stop codon in the mature F5 mRNA. Although platelet FV antigen was detectable by immunoprecipitation followed by Western blotting, no FV activity could be demonstrated in the proband's plasma or platelets with a prothrombinase-based assay. Moreover, no thrombin generation was observed in PRP triggered with 1-50 pm tissue factor (even in the presence of platelet agonists), whereas an acquired FV inhibitor was excluded. Clot formation in the proband's whole blood, as assessed by thromboelastometry, was markedly delayed but not abolished. This is the first report of a pathogenic deep-intronic mutation in the F5 gene. Our findings indicate that the minimal FV requirement for viability is extremely low and suggest that thrombin generation in PRP may predict bleeding tendency in patients with undetectable plasma FV.

Coagulation factor content of plasma produced from whole blood stored for 24 hours at ambient temperature: results from an international multicenter BEST Collaborative study

There is increasing international interest in producing components from blood that has been stored at room temperature for 24 hours. The lack of comprehensive data on the quality of plasma produced from blood stored in this way led to this international study. A total of 128 units of whole blood were pooled in groups of four and split to produce 32 sets of four identical blood units that were processed either within 8 hours of blood collection or after 24-hour storage at 18 to 25°C. Storage of whole blood for 24 hours resulted in a 23% decrease in the activity of Factor (F)VIII, but not significant loss of activity of coagulation factors FV, FVII, FXI, FXII, fibrinogen, antithrombin, or von Willebrand factor. There was a small, but significant decrease in levels of FII, FIX, and FX (all <5%) as well as protein C (6%) and free protein S activity (14%). The ability of plasma to generate thrombin after 24-hour storage as whole blood was unaltered, as assessed by real-time thrombin generation tests as was the rate and strength of clot formation by rotational thombelastometry. Levels of all coagulation factors measured were above 0.50 U/mL in plasma produced from whole blood stored for 24 hours. These data show that there is minimal effect of storing whole blood at ambient temperature for 24 hours on the coagulation activity of plasma and that this is an acceptable alternative to producing plasma on the day of blood collection.

Cellular regulation of blood coagulation: a model for venous stasis

AbstractWe have adapted the corn-trypsin inhibitor whole-blood model to include EA.hy926 as an endothelium surrogate to evaluate the vascular modulation of blood coagulation initiated by relipidated recombinant tissue factor (rTf) and a cellular Tf surrogate, lipopolysaccharide (LPS)-stimulated THP1 cells (LPS-THP-1). Compared with bare tubes, EA.hy926 with rTf decreased the rate of thrombin formation, ITS accumulation, and the production of fibrinopeptide A. These phenomena occurred with increased rates of factor Va (fVa) inactivation by cleavages at R506 and R306. Thus, EA.hy926 provides thrombin-dependent protein C activation and APC fVa inactivation. Comparisons of rTf with LPS-THP-1 showed that the latter gave reduced rates for TAT formation but equivalent fibrinopeptide A, and fV activation/inactivation. In the presence of EA.hy926, the reverse was obtained; with the surrogate endothelium and LPS-THP-1 the rates of TAT generation, fibrinopeptide release, and fV activation were almost doubled, whereas cleavage at R306 was equivalent. These observations suggest cooperativity between the 2 cell surrogates. These data suggest that the use of these 2 cell lines provides a reproducible quasi-endothelial quasi-inflammatory cytokine-stimulated monocyte system that provides a method to evaluate the variations in blood phenotype against the background of stable inflammatory cell activator and a stable vascular endothelial surrogate.

Lyophilised plasma: evaluation of clotting factor activity over 6 days after reconstitution for transfusion

AimsLittle is known about long-term stability of clotting factors in dissolved human lyophilised plasma. This study evaluated clotting factor and inhibitor activity in reconstituted lyophilised plasma after storage for up...

Plasma activity of individual coagulation factors, hemodilution and blood loss after cardiac surgery: A prospective observational study

BackgroundHemodilution and consumption of coagulation factors during cardiopulmonary bypass has been suggested to contribute to bleeding complications after cardiac surgery. The aim was to describe the activity of individual coagulation factors after CABG in relation to hemodilution and postoperative bleeding. Materials and MethodsPlasma concentrations of fibrinogen and plasma activity of FII, FV, FVII, FVIII, FIX, FX, FXI and FXIII adjusted for hemodilution were analysed in 57 CABG patients before, and 2h and 24h after surgery. Postoperative bleeding was registered and correlations to coagulation factor activity were calculated. ResultsAdjusted plasma concentration of fibrinogen (-14±6%), and plasma activity of FII (-9±6%), FV (-13±8%), FX (-13±7%) and FXIII (-9±14%) were reduced two hours after surgery compared to baseline (all p<0.001). FVII (+3±12%, p=0.34) and FXI (+1±19%, p=0.50) were unchanged, while FVIII (+23±44%, p=0.006) and FIX (+23±17%, p<0.001) increased. Twenty-four hours after surgery fibrinogen (+45±27%), FVIII (+93±66%) and FIX (+33±26%) were all increased (all p<0.001), while FVII (-37±14%, p<0.001), FXI (-4±18%, p=0.02) and FXIII (-6±15%, p=0.004) were decreased.Median postoperative blood loss was 380ml/12h. There were significant inverse correlations between postoperative blood loss and fibrinogen concentration 2h after surgery (r=-0.33, p=0.019) and between postoperative blood loss and pre- and postoperative FXIII activity (r=-0.34, p=0.009 and r=-0.41, p=0.003, respectively), but not between blood loss and any of the other factors. ConclusionsThere is a marked dissociation in plasma activity of individual coagulation factors after CABG. Plasma concentration of fibrinogen and factor XIII activity correlates inversely to postoperative blood loss after CABG.

Conversion to the buffy coat method and quality of frozen plasma derived from whole blood donations in Canada

Canada converted from the platelet-rich plasma (PRP) method to the buffy coat (BC) method of processing whole blood donations between 2006 and 2008. We measured coagulation variables in plasma units during this transition, in 2006 (PRP only), 2007 (BC and PRP), and 2008 (BC only) to test the hypothesis that this conversion would not affect frozen plasma (FP) quality. Fresh-frozen plasma (FFP; frozen within 8 hr of collection) or FP (frozen within 24 hr of collection) units were shipped on dry ice from 12 plasma manufacturing sites, thawed, and characterized using an automated coagulation analyzer, at a single testing site. FP made by the BC method (FP-BC) exhibited fibrinogen, Factor (F)V, ABO-matched FVIII, and antithrombin levels at least as high as FP made by the PRP method (FP-PRP) and supported global clotting, as measured by prothrombin time or activated partial thromboplastin time, to an indistinguishable extent as FP-PRP. FP-BC and FP-PRP did not differ in ABO-matched FVIII levels, but both contained 30% to 35% less FVIII than FFP. There was no discernible effect of the site of manufacturing on plasma quality. FP-BC units leukoreduced by centrifugation contained more FV activity than those leukoreduced by filtration, but the difference was unlikely to be of clinical significance. Our data suggest that no reduction in FP quality, at least in the characteristics we tested, accompanied the switch from the PRP to the BC method processing of whole blood donations in Canada.

Coagulation procofactor activation by factor XIa.

In the extrinsic pathway, the essential procofactors factor (F) V and FVIII are activated to FVa and FVIIIa by thrombin. In the contact pathway and its clinical diagnostic test, the activated partial thromboplastin time (APTT) assay, the sources of procofactor activation are unknown. In the APTT assay, FXII is activated on a negatively charged surface and proceeds to activate FXI, which activates FIX upon the addition of Ca(2+). FIXa feeds thrombin generation through activation of FX. FIXa is an extremely poor catalyst in the absence of its FVIIIa cofactor, which, in the intrinsic FXase complex, increases FXa generation by approximately 10(7). One potential APTT procofactor activator in this setting is FXIa. To test the hypothesis that FXIa can activate FVIII and FV. Recombinant FVIII and plasma FV were treated with FXIa, and the activities and integrities of each procofactor were measured using commercial clotting assays and sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE). Kinetic analyses of FXIa-catalyzed activation and inactivation of FV and FVIII are reported, and the the timing and sites of cleavage are defined. FXIa activates both procofactors at plasma protein concentrations, and computational modeling suggests that procofactor activation during the preincubation phase of the APTT assay is critical to the performance of the assay. As the APTT assay is the primary tool for the diagnosis and management of hemophilias A and B, as well as in the determination of FVIII inhibitors, these findings have potential implications in the clinical setting.

HD1, a thrombin- and prothrombin-binding DNA aptamer, inhibits thrombin generation by attenuating prothrombin activation and thrombin feedback reactions

HD1, a DNA aptamer, binds exosite 1 on thrombin and blocks its clotting activity. Because HD1 also binds prothrombin and inhibits its activation by prothrombinase, we hypothesised that HD1 would be a more potent inhibitor of coagulation than other exosite 1-directed ligands, such as Hir(54-65)(SO(3)(-)). Supporting this concept, the effect of HD1 on the prothrombin time and activated partial thromboplastin time was two-fold greater than that of Hir(54-65)(SO(3)(-)) even though both agents inhibited thrombin-mediated factor (F) V and FVIII activation to a similar extent. In thrombin generation assays, HD1 (a) delayed the lag time, (b) reduced peak thrombin concentration, and (c) decreased endogenous thrombin potential to a greater extent than Hir54-65(SO(3)(-)). To eliminate thrombin feedback, studies were repeated in FV- and/or FVIII-deficient plasma supplemented with FVa and/or FVIIIa. Only HD1 prolonged the lag time in FV- and FVIII-deficient plasma supplemented with FVa and FVIIIa. In contrast, HD1 and Hir54-65(SO(3)(-)) inhibited the lag time in FVIII-deficient plasma supplemented with FVIIIa and in normal plasma. The more potent anticoagulant properties of HD1, therefore, reflect its capacity to attenuate FV activation by thrombin and inhibit prothrombinase assembly. These findings identify prothrombin as a potential target for new anticoagulants.