Haemostasis and Thrombosis

SummaryA score that can accurately determine the risk of major bleeding during anticoagulant therapy may help to make decisions on anticoagulant use. RIETE is an ongoing registry of consecutive patients with acute venous thromboembolism (VTE). We composed a score to predict the risk for major bleeding within three months of anticoagulant therapy. Of 19,274 patients enrolled, 13,057 (67%) were randomly assigned to the derivation sample, 6,572 to the validation sample. In the derivation sample 314 (2.4%) patients bled (fatal bleeding, 105). On multivariate analysis, age >75 years, recent bleeding, cancer, creatinine levels >1.2 mg/dl, anemia, or pulmonary embolism at baseline were independently associated with an increased risk for major bleeding. A score was composed assigning 2 points to recent bleeding, 1.5 to abnormal creatinine levels or anemia, 1 point to the remaining variables. In the derivation sample 2,654 (20%) patients scored 0 points (low risk); 9,645 (74%) 1–4 poin...

Summary. Background: Protein Z (PZ) serves as a cofactor for activated factor X inhibition by the PZ-dependent protease inhibitor. In vivo and in vitro studies aimed at investigating the role of PZ levels in venous thombosis have produced conflicting results. Objectives: We investigated whether reduced PZ levels and PZ gene common variants are associated deep vein thrombosis (DVT). Patients and methods: In 197 patients with DVT and in 197 age-matched and sex-matched controls, PZ plasma levels and gene polymorphisms were evaluated by means of an enzyme-linked immunosorbent assay and direct cycle sequence analysis. Results: Similar PZ levels were found in controls (1.44; SD 0.63 μg mL−1) and in patients (1.44; SD 0.96 μg mL−1). The incidence of PZ levels below the 5.0 (0.52 μg mL−1) or the 2.5 percentile of controls (0.47 μg mL−1) was higher in patients (10.2% and 8.7%, respectively) than in controls {4.1% [odds ratio (OR) 2.7, 95% confidence interval (CI) 1.2–7.3], and 2.0% (OR 4.6, 95% CI 1.5–13.9), respectively}. This relationship was independent of the effect of age, sex, and factor V Leiden and FII A20210 alleles [OR 2.8 (95% CI 1.1–7.3), and OR 4.9 (95% CI 1.4–17.3)]. PZ levels were associated with the intron C G-42A and the intron F G79A polymorphisms in cases (r2 = 0.129) and in controls (r2 = 0.140). However, frequencies of the PZ gene polymorphisms were similar in the two groups and were not associated with very low PZ levels. Conclusions: The present data suggest an association between very low PZ plasma levels and the occurrence of DVT, with PZ gene polymorphisms contributing little to this relationship.

To cite this article: Ulrichts H, Harsfalvi J, Bene L, Matko J, Vermylen J, Ajzenberg N, Baruch D, Deckmyn H, Tornai I. A monoclonal antibody directed against human von Willebrand factor induces type 2B-like alterations. J Thromb Haemost 2004; 2: 1622-28.

SummaryThe natural history of patients with venous thromboembolism (VTE) who develop a major bleeding complication while on anticoagulant therapy is not well known. RIETE is a prospective registry of consecutive patients with symptomatic, objectively confirmed, acute VTE. The clinical characteristics, treatment decisions and outcome of all VTE patients who had major bleeding during the first three months of anticoagulant therapy were retrospectively studied. As of January 2007, 17,368 patients were included in RIETE. Of these, 407 (2.3%) had major bleeding during the study period: 144 gastrointestinal, 119 haematoma, 51 intracranial, 43 genitourinary, 50 other. In 286 (69%) patients anticoagulant therapy was discontinued, in 74 (18%) not modified, in 38 (9.1%) a vena cava filter was inserted. During the first 30 days after bleeding, 24 (5.9%) patients re-bled, 20 (4.9%) had recurrent VTE, 133 (33%) died. Of these, 75 died of bleeding, 12 of recurrent pulmonary embolism. Most deaths ...

To cite this article: Iorio A., Marcucci M., Makris M. Concentrate-related inhibitor risk: is a difference always real? J Thromb Haemost 2011; 9: 2176-9. See also Aledort LM, Navickis RJ, Wilkes MM. Can B-domain deletion alter the immunogenicity of recombinant factor VIII? A meta-analysis of prospective clinical studies. This issue, pp 2180-92.

Hemorheologic tests were performed in 52 obese healthy subjects (OB; 31 females, age range 14-56,), with body mass index (BMI) ranging between 32-54, before (TO) and after 3 months (T3) of VLCD (470 Kcal/day), and in a control group (CG) of 28 (12 females) non obese age-matched individuals. Compared to CG male OBs had higher levels of Hematocrit (Ht, p< 0,05), plasma viscosity (PLV, p<O,OOl), erythrocyte aggregation index (EAI, Rheoaggregometer Myrenne, p<O,OOl) and fibrinogen (Fgn, p<O,OOl). Female OBs had higher PLV (p<O,Ol), EAI (pcO,O5) and Fgn @<O,OOl) levels. Three months VLCD induced a significant reduction in BMI (from 37.920.2 to 32.021.1, p<O.OOl) and EAI (from 35.421.9 AU to 28.621.9, p<O.OOl). In male OBs Ht was also reduced (~~0.05). In female OBs a reduction in total proteins @<O.Ol) with increased albumin/globulin ratio (pcO.001) was recorded. No changes in Fgn and PLV levels were observed. In conclusion, marked obesity is associated with alterations of some hemorheologic parameters; a prolonged period of very low calorie diet improved erythrocyte aggregability (probably due to improved albumin/globulin ratio) while not affecting Fgn and PLV levels. C 182 K2tu-PA is a hybrid plasminogen activator linking the kringle 2 domain of t-PA to the catalytic protease domain scu-PA. Kptu-PA has a plasma half-life of over 30 minutes. The aim of this study was to compare the effects of bolus doses of &PA and K2tu_PA, on: 1) lysis of pm-formed thrombi (fibrinolysis), 2) accretion of new fibrin on pre-existing thrombi during fibrinolysis (thrombus growth), 3) systemic plasma proteolysis and blood Ices from a standard wound. A jugular vein thrombosis and an ear bleeding model were adopted in rabbits. Saline produced 11*2% fibrindysis. &PA, 0.2 mg/Kg, 0.4 mg/kg and 0.8 mg/Kg produced 35*4%, 54*4Oh and 78&% fibrinolysis, respectively. K2tu-PA! at the same doses, produced 396%, 576% and 83&% fibrinolysis, respectively. Injection of saline was followed by an accretion of 56.4k5.9 pg of radioactive new f&tin on the thrombi. The injection of the three increasing doses of &PA was followed by an accretion of 54.9k5.3 pg, 49.lti.lpg and 47.2k4.8 pg. The injection of three increasing doses of K2tu-PA was fdlowed by an accretion of pg. At each of the three doses, K2tu-PA was more effective than &PA in reducing the accretion of new fibrin on the thrombi (~0.01) and, as a consequence, in reducing thrombus weight (pcO.01). The two lower doses of rt-PA and K2tu-PA did not produce systemic proteolysis and bleeding. The highest dose of K2tu-PA produced a statistically significant more intense systemic proteolysis and bleedi n! This study demonstrates that bolus doses of K2tu-P than the highest dose of rt-PA. and &PA produce a similar degree of fibrinolysis. K2tu-PA is more efficient than rt-PA in inhibiting accretion of new fibrin on the thrombi during thrombolysis. The potential increased risk of bleeding with a bolus of high doses of l$tu-PA has to be seen in view of the advantage of avoiding the concomitant use of heparin.

Currently, molecular diagnosis of haemophilia A and B (HA and HB) highlights the excess risk-inhibitor development associated with specific mutations, and enables carrier testing of female relatives and prenatal or preimplantation genetic diagnosis. Molecular testing for HA also helps distinguish it from von Willebrand disease (VWD). Next-generation sequencing (NGS) allows simultaneous investigation of several complete genes, even though they may span very extensive regions. This study aimed to evaluate the usefulness of a molecular algorithm employing an NGS approach for sequencing the complete F8, F9 and VWF genes. The proposed algorithm includes the detection of inversions of introns 1 and 22, an NGS custom panel (the entire F8, F9 and VWF genes), and multiplex ligation-dependent probe amplification (MLPA) analysis. A total of 102 samples (97 FVIII- and FIX-deficient patients, and five female carriers) were studied. IVS-22 screening identified 11 out of 20 severe HA patients and ...

Alpha granule release plays an important role in propagating a hemostatic response upon platelet activation. We evaluated the ability of various agonists to cause a granule release in platelets. Alpha granule release was measured by determining P-selectin surface expression in aspirin-treated washed platelets. ADP-induced P-selectin expression was inhibited both by MRS 2179 (a P2Y1 selective antagonist) and AR-C69931MX (a P2Y12 selective antagonist), suggesting a role for both Ga q and Ga i pathways in ADP-mediated a granule release. Consistent with these observations, the combination of serotonin (a Ga q pathway stimulator) and epinephrine (a Ga z pathway stimulator) also caused a granule release. Furthermore, U46619-induced P-selectin expression was unaffected by MRS 2179 but was dramatically inhibited by AR-C69931, indicating a dominant role for P2Y12 in U46619mediated a granule release. Additionally, the Ga 12/13 -stimulating peptide YFLLRNP potentiated a granule secretion in combination with either ADP or serotonin/epinephrine costimulation but was unable to induce secretion by itself. Finally, costimulation of the Ga i and Ga 12/13 pathways resulted in a significant dose-dependent increase in a granule release. We conclude that ADP-induced a granule release in aspirin-treated platelets occurs through costimulation of Ga q and Ga i signaling pathways. The P2Y12 receptor plays an important role in thromboxane A 2 -mediated a granule release, and furthermore activation of Ga 12/13 and Ga q signaling pathway can cause a granule release.

Summary.  Background: The metabolism of estrogen contained within hormone replacement therapy (HRT) is influenced by the route of administration, and this may affect the risk of venous thromboembolism. Thrombin generation, a global coagulation assay, is a marker of hypercoagulability and is of potential use in determining the thrombotic risk associated with particular HRT administration routes. Objectives: To determine whether any effect of oral and transdermal HRT on thrombin generation is related to the plasma estrogen profile. Methods: We investigated the effects of oral, transdermal and no HRT (controls) in 52, 39 and 52 postmenopausal women, respectively, on thrombin generation, standard markers of thrombophilia, estradiol level and estrone level. Results: All parameters of thrombin generation were altered in women using oral HRT as compared with controls (P < 0.001 for all comparisons). No such differences were found in women using transdermal HRT. Estrone levels correlated with peak thrombin generation (R = 0.451, P < 0.001) in women using oral HRT, but there was no correlation in women using the transdermal route. Conclusions: Thrombin generation is significantly increased in women who use HRT administered by the oral route. This is probably mediated by the hepatic first-pass metabolism of estrone, the main metabolite of oral estradiol, which is avoided by the transdermal route. The effect of estrone on thrombin generation may provide the explanation for the higher thrombotic risk seen in women using oral rather than transdermal HRT.

SummaryWomen with a history of venous thromboembolism (VTE), thrombophilia or both may be at increased risk of thrombosis during pregnancy, but the optimal management strategy is not well defined in clinical guidelines because of limited trial data. A strategy of risk assessment and heparin prophylaxis was evaluated in pregnant women at increased risk of VTE. In a prospective trial (Efficacy of Thromboprophylaxis as an Intervention during Gravidity [EThIG]), 810 pregnant women were assigned to one of three management strategies according to pre-defined risk factors related to history of VTE and thrombophilic profile. Low-risk women (group I), received 50–100 IU dalteparin/ kg body weight/ day for 14 days postpartum, or earlier when additional risk factors occurred. Women at high (group II) or very high risk (group III) received dalteparin from enrolment until six weeks postpartum (50–100 IU and 100–200 IU/ kg/ day, respectively). Objectively confirmed, symptomatic VTE occurred in 5/...

This review summarizes the nature of ambient air pollutants, which are either gaseous or particulate of various sizes, the latter determining their penetration into the body, the smallest even translocating from the lung into the systemic circulation. It presents the epidemiological evidence linking air pollution to overall mortality, cardiovascular mortality and myocardial infarction, making the distinction between acute and chronic exposure to the pollutants. It reviews mechanistic investigations that have evaluated the links among exposure to pollutants, thrombosis, pulmonary inflammation, arterial vasoconstriction and heart rate variability. It concludes by attempting to integrate current epidemiological and mechanistic observations into a pathophysiological framework that links ambient air pollution to acute myocardial infarction and cardiovascular mortality.

Results: Haemoglobin concentration of 6.22±1.75 g/dl and HCT of 18.45±6.43% for SCA subjects in VOC; Hb of 7.42±1.36 g/dl and HCT of 22.83±4.68% in steady state were significantly decreased(p<0.01) compared with Hb(13.0±1.04 g/dl and HCT(41.09±3.50%) for HbAA controls. However, plasma FPA of 680.99 ± 411.37 ng/ml, WBC of 19.44±14.88 x10 9 /L, Plt of 292.72±148.57 x10 9 /L, APTT of 52.24±5.34sec. for SCA subjects in VOC and Plasma FPA of 449.67 ± 310.01 ng/ml, WBC of 11.84±7.67 x10 9 /L, Plt of 292.72±148.57 x10 9 /L, APTT of 47.76±4.80secs in steady state were significantly increased when compared with FPA(163.52 ± 86.26ng/ml), WBC(5.15±1.24 x10 9 /L), Plt(173.44±59.90 x10 9 / L), APTT(37.75±1.41secs) for HbAA controls. Conclusion: Fibrinolysis is not significantly increased in SCA either in the steady state or during VOC. Fibrinopeptide A assay appears to be of value in the assessment of VOC in sickle cell anaemia.

SummaryCongenital afibrinogenemia (CAF) is a rare coagulation disorder characterized by very low or unmeasurable levels of functional and immunoreactive fibrinogen in plasma, associated with a hemorrhagic phenotype of variable severity. It is transmitted as an autosomal recessive trait (prevalence 1:1,000,000) and is invariantly associated with mutations affecting one of the three fibrinogen genes (FGA, FGB, and FGG, coding for Aα, Bβ, and γ chain, respectively). Fibrinogen is secreted by hepatocytes as a hexamer composed of two copies of each chain; the lack of one chain has been demonstrated to prevent its secretion. Most genetic defects causing afibrinogenemia are point mutations, where- as only three large deletions have been identified so far, all affecting the FGA gene. We here report the molecular characterization of six unrelated afibrinogenemic patients leading to the identification of eight different mutations, four hitherto unknown: a 4.1-Kb large deletion involving exon ...

Summaryα2-Antiplasmin (α2-AP) is the main physiological plasmin inhibitor in mammalian plasma. As a first step toward the generation of α2-AP deficient mice, the murine α2-AP 1 gene was characterized and a targeting vector for homologous recombination in embryonic stem (ES) cells constructed. Alignment of nucleotide sequences obtained from genomic subclones allowed location of exons 2 through 10 of the α2-AP 1gene, but failed to identify the 5’ boundary of exon 1. Compared to the human gene, exons 2 through 9 in the murine gene have identical size and intron-exon boundaries obeying the GT/AG rule. The 5’ boundary of exon 10 is identical in both genes while the 3’ non-coding region is 64 bp longer in the human gene. Introns 2,3,6 and 8 have similar sizes in the mouse and human genes; intron 1 is 6-fold smaller, introns 5, 7 and 9 are 2- to 3-fold smaller, whereas intron 4 is about 2-fold larger in the mouse gene. Compared to the human 5’ flanking sequence, an insertion of a simple re...

Matrix γ-carboxyglutamate (Gla) protein (MGP) is an important local inhibitor of vascular calcification, which can undergo two post-translational modifications: vitamin K-dependent γ-glutamate carboxylation and serine phosphorylation. While carboxylation is thought to have effects upon binding of calcium-ions, phosphorylation is supposed to affect the cellular release of MGP. Since both modifications can be exerted incompletely, various MGP species can be detected in the circulation. MGP levels were measured with two commercially available competitive and two novel sandwich assays in healthy controls, in patients with rheumatic disease, aortic valve disease, and end-stage renal disease, as well as in volunteers after vitamin K supplementation (VKS) and treatment with vitamin K antagonists (VKA). Major differences were found between the MGP assays, including significantly different behaviour with regard to vascular disease and the response to VKA and VKS. The dual-antibody assay measuring non-phosphorylated, non-carboxylated MGP (dp-ucMGP) was particularly sensitive for these changes and would be suited to assess the vascular vitamin K status. We conclude that the different assays for particular circulating MGP species allows the assessment of various aspects of the MGP system.

Despite advances in secondary prevention strategies in patients with cardiovascular disease, the residual risk of recurrent atherothrombotic events remains high. Dual-antiplatelet therapy is the standard of care for secondary prevention in patients with acute coronary syndrome (ACS), whereas single antiplatelet therapy, generally with aspirin, is the standard of care for secondary prevention in stable patients with coronary artery disease (CAD), peripheral artery disease (PAD), or cerebrovascular disease. However, atherosclerotic plaque disruption not only triggers platelet activation but also results in thrombin generation because of tissue factor exposure. Therefore, blocking both pathways by combining antiplatelet therapy with an anticoagulant, or dual pathway inhibition (DPI), has the potential to be more effective than inhibiting either pathway alone. The benefit of DPI has been demonstrated in the ATLAS ACS 2-TIMI 51, COMPASS, and VOYAGER PAD trials, where the combination of r...

To cite this article: Li Y, Bezemer ID, Rowland CM, Tong CH, Arellano AR, Catanese JJ, Devlin JJ, Reitsma PH, Bare LA, Rosendaal FR. Genetic variants associated with deep vein thrombosis: the F11 locus. J Thromb Haemost 2009; 7: 1802-8. 1.59). We found that rs2289252 was also associated with FXI levels, as has been previously reported for rs2036914; these two SNPs remained associated with DVT with somewhat attenuated risk estimates after adjustment for FXI levels. Conclusion: Two SNPs, rs2289252 and rs2036914 in F11, appear to independently contribute to the risk of DVT, a contribution that is explained at least in part by an association with FXI levels.

Hospitalized patients with acute medical conditions are at significant risk of venous thromboembolism (VTE): approximately 10-30% of general medical patients may develop deep-vein thrombosis or pulmonary embolism, and the latter is a leading contributor to deaths in hospital. Despite consensus-group recommendations that at-risk medical patients should receive thromboprophylaxis, there is currently no consensus as to which patients are at risk, and many patients may not receive appropriate thromboprophylaxis. This paper reviews evidence for the risk of VTE associated with different medical conditions and risk factors, and presents a risk-assessment model for risk stratification in medical patients. Medical conditions associated with a moderate to high risk of VTE include cardiac disease, cancer, respiratory disease, inflammatory bowel disease, and infectious diseases. Importantly, analyses of data from the MEDENOX study show that thromboprophylaxis significantly reduces the risk of V...

To cite this article: Harenberg J. The safety of dosing dalteparin based on actual body weight for the treatment of acute venous thromboembolism in obese patients: a rebuttal. J Thromb Haemost 2005; 3: 1550. See also Al-Yaseen E, Wells PS, Anderson J, Martin J, Kovacs MJ. The safety of dosing dalteparin based on actual body weight for the treatement of acute venous thromboembolism in obese patients. J Thromb Haemost 2005; 3: 100-02.

... 7 Lopaciuk S, Bykowska K, Kwiecinski H, Czlonkowska A, Kuczynska-Zardzewialy A. Protein Z in young survivors of ischemic stroke. ... J Neurol 2003; 250: 63–6. 10 Adams HP Jr, Bendixen BH, Kappelle LJ, Biller J, Love BB, Gordon DL, Marsh EE III and the TOAST Investigators. ...

Obesity, and especially excessive visceral adipose tissue accumulation, is considered as a low-grade inflammatory state that is responsible for adipocyte dysfunction and associated metabolic disorders. Adipose tissue displays endocrine functions by releasing pro- or anti-inflammatory bioactive molecules named adipokines. An altered expression of these molecules, provoked by obesity or adipocyte dysregulation, contributes to major metabolic diseases such as insulin resistance and type 2 diabetes mellitus that are important risk factors for cardiovascular disease. However, obesity is also characterised by the expansion of perivascular adipose tissue that acts locally via diffusion of adipokines into the vascular wall. Local inflammation within blood vessels induced by adipokines contributes to the onset of endothelial dysfunction, atherosclerosis and thrombosis, but also to vascular remodelling and hypertension. A fast expansion of obesity is expected in the near future, which will ra...

Oral anticoagulants are a mainstay of cardiovascular therapy, and for over 60 years vitamin K antagonists (VKAs) were the only available agents for long-term use. VKAs interfere with the cyclic inter-conversion of vitamin K and its 2,3 epoxide, thus inhibiting γ-carboxylation of glutamate residues at the amino-termini of vitamin K-dependent proteins, including the coagulation factors (F) II (prothrombin), VII, IX and X, as well as of the anticoagulant proteins C, S and Z. The overall effect of such interference is a dose-dependent anticoagulant effect, which has been therapeutically exploited in heart disease since the early 1950s. In this position paper, we review the mechanisms of action, pharmacological properties and side effects of VKAs, which are used in the management of cardiovascular diseases, including coronary heart disease (where their use is limited), stroke prevention in at-rial fibrillation, heart valves and/or chronic heart failure. Using an evidence-based approach, we describe the results of completed clinical trials, highlight areas of uncertainty, and recommend therapeutic options for specific disorders. Although VKAs are being increasingly replaced in most patients with non-valvular atrial fibrillation by the new oral anticoagulants, which target either thrombin or FXa, the VKAs remain the agents of choice for patients with atrial fibrillation in the setting of rheumatic valvular disease and for those with mechanical heart valves.

Vascular injury leads to formation of a structured thrombus as a consequence of platelet activation and aggregation, thrombin and fibrin formation, and trapping of leukocytes and red cells. This review summarises current evidence for heterogeneity of platelet responses and functions in the thrombus-forming process. Environmental factors contribute to response heterogeneity, as the platelets in a thrombus adhere to different substrates, and sense specific (ant)agonists and rheological conditions. Contraction of platelets and interaction with fibrin and other blood cells cause further response variation. On the other hand, response heterogeneity can also be due to intrinsic differences between platelets in age and in receptor and signalling proteins. As a result, at least three subpopulations of platelets are formed in a thrombus: aggregating platelets with (reversible) integrin activation, procoagulant (coated) platelets exposing phosphatidylserine and binding coagulation factors, an...

To cite this article: Rossetti LC, Radic CP, Larripa IB, De Brasi CD. Developing a new generation of tests for genotyping hemophilia-causative rearrangements involving int22h and int1h hotspots in the factor VIII gene. J Thromb Haemost 2008; 6: 830-6.

Using a systems approach to profile self-limited inflammatory exudates, we identified three novel families of lipid-derived mediators, coined the resolvins, protectins and most recently, the maresins that control both the magnitude and duration of inflammation. The mapping of these endogenous resolution circuits provides new avenues to probe the molecular basis of many widely occurring inflammatory diseases. This article focuses on our recent advances on the functional metabolomics of this novel genus of specialized pro-resolving mediators (SPM). SPM include resolvins, protectins and maresins and are biosynthesized from essential omega-3 fatty acid precursors. Each possesses potent multi-pronged actions that proved to be stereoselective with human cells and in animal disease models. Resolvins and protectins are also produced in bone marrow. Together, these findings suggest that defective resolution mechanism(s) may underlie some chronic inflammatory diseases. Moreover, identification of functional SPM biosynthesized during inflammation-resolution indicates that resolution is an active process.

Platelet secretion not only drives thrombosis and haemostasis, but also mediates a variety of other physiological and pathological processes.  The ubiquitous SNARE machinery and a number of accessory proteins have been implicated in regulating secretion in platelets.  Although several platelet SNAREs have been identified, further members of the SNARE family may help fine-tune platelet secretion.  In this study I identified expression of t-SNAREs VTI1A, VTI1B (Qb SNAREs) and STX8 (Qc SNARE) in human and mouse platelets.  Those ‘novel’ SNAREs were able to interact with each other and previously reported SNAREs VAMP8 (R-SNARE) and STX11 (Qa SNARE), thus suggesting existence of a secondary SNARE complex in addition to the widely accepted SNAP23-VAMP8-STX11 complex.  In following mouse studies, whereas neither gene was found to
be essential for α-granule or lysosome secretion, Stx8-/- platelets showed a significant defect in dense granule secretion and aggregation, that was most pronounced at intermediate concentrations of agonists.  Addition of exogenous ADP could rescue the aggregation defect but failed to restore dense granule secretion, suggesting the defect lies in the ‘primary’ secretory pathway.  Pretreatment with P2Y receptors antagonists reduced secretion and aggregation to the same extent in WT and Stx8-/- platelets, suggesting that the ADP-driven positive feedback mechanism was not defective in Stx8-/- platelets.  In addition, STX8 was found to play a role in regulating pro-coagulant activity suggesting novel roles for SNAREs in platelets.  Neither Vti1a-/- nor Vti1b-/- showed any
significant defects, suggesting complementarity between those homologues in
platelets.  STX8 therefore specifically contributes to dense granule secretion and
represents another member of a growing family of genes that play distinct roles
in differentially regulating granule release from platelets.  Taken together, data
presented in this Thesis not only provides first evidence of an additional SNARE complex present in platelets but also suggests novel roles for SNAREs in regulation of thrombosis and haemostasis