Haemostasis最新文献

Thrombin formation and blood platelet reactions are intimately linked in haemostasis and in thrombosis. In vivo, procoagulant phospholipids required for the coagulation mechanism are mainly provided by activated platelets, and thrombin is the most potent platelet activator. To study these interactions, an ancient tool of coagulation physiology, the thrombin generation test, was revived and the results obtained were reviewed. The amount of thrombin activity that develops, expressed as the endogenous thrombin potential (the area under the thrombin generation curve), is influenced by the clotting factors (except XII and XIII), the activated protein C system and natural inhibitors on the one hand and by platelet activity on the other. The platelet reactions that we found to be involved are induced by thrombin via glycoprotein (GP) IIb/IIIa activation and by fibrin via interaction with GPIb. von Willebrand factor is crucial in both reactions and therefore an obligatory factor for normal thrombin generation in the presence of platelets. All antithrombotics, be it anticoagulants (e.g. OAC, all heparins or hirudin) or antiplatelet drugs (aspirin, GPIIb/IIIa blockers) diminish thrombin generation.

Epidemiological evidence suggests a positive correlation between the number of PMN and the risk of ischemic vascular disease. The observation that activated PMN induce platelet activation my provide some biological plausibility to the role of PMN in thrombogenesis. Between other PMN products, cathepsin G, a protease released during PMN activation, is a potent platelet agonist. However, the antiproteinases present in plasma could virtually abolish its activity. Indeed it was shown that, when PMN were stimulated after interaction with platelets in mixed cell population, P-selectin-mediated platelet-PMN adhesion may result in the formation of a sequestered microenvironment in which cathepsin G activity is protected by antiproteases. P-selectin-mediated adhesion was also shown to facilitate the transcellular metabolism of arachidonic acid, resulting in increased production of both thromboxane B2 and leukotriene C4. PMN adhesion to activated platelets in mixed cell suspensions subjected to high shear rate can be modeled as an adhesion cascade involving a P-selectin-dependent recognition step followed by an adhesion-strengthening interaction mediated by the beta(2)-integrin Mac-1. Moreover, an intermediate tyrosine-kinase-dependent signal regulating beta(2)-integrin adhesiveness is required. Indeeed activated platelets express not only P-selectin but also different beta(2)-integrin ligands including fibrinogen and ICAM-2. Some of the functional responses elicited by P-selectin on PMN could be prevented by specific antibody to the P-selectin glycoprotein ligand-1, indicating that this adhesive receptor is able to transduce an 'outside-in' signal when engaged by the ligand. By using activated platelets, P-selectin-expressing CHO cells and soluble recombinant P-selectin, P-selectin was shown to trigger protein tyrosine phosphorylation in PMN and the tyrosine kinase-dependent function of Mac-1. In conclusion, adherence of activated platelets to PMN may be a key event in the sequence of thrombus formation. The recognition of the essential contribution of PMN beta(2)-integrins in addition to P-selectin in platelet-PMN adhesion provides an additional evidence to the broad range of function and mechanisms in which PMN integrins are involved and may be potential targets for pharmacological intervention.

From the bloodsucking bug Dipetalogaster maximus, a protein with anticoagulant activity was isolated and biochemically characterized. The isolated protein, named dipetalogastin, possesses an average molecular mass of 11.8 kD. Its N-terminal sequence shows homology to rhodniin, a thrombin inhibitor isolated from the bug Rhodnius prolixus. The in vitro anticoagulant activity of dipetalogastin occurs via the inhibition of thrombin. The anticoagulant and thrombin inhibitory potency of dipetalogastin is comparable to that of recombinant hirudin. Its specific thrombin inhibitory activity is 9,300 antithrombin units/mg protein. Dipetalogastin forms only 1:1 molar complexes with thrombin. It is a tight-binding inhibitor of thrombin possessing a dissociation constant of 125 fM. It does not inhibit factor Xa or alpha-chymotrypsin and only weakly inhibits trypsin.

Antiphospholipid antibodies are strongly associated with thrombosis and appear to be the most common of the acquired blood protein defects causing thrombosis. Based upon our experience, approximately 25% of patients with unexplained venous thrombosis, approximately 60% of patients with cerebrovascular thrombosis, approximately 37% of patients with transient ischemic attacks, approximately 18% with premature coronary artery thrombosis and approximately 60% of patients with recurrent fetal loss (recurrent miscarriage syndrome) harbor antiphospholipid antibodies. Although the precise mechanism(s) whereby antiphospholipid antibodies alter hemostasis to induce a hypercoagulable state remain unclear, several theories have been advanced. Since the aPTT is unreliable in patients with lupus anticoagulant and is not usually prolonged in patients with anticardiolipin antibodies, definitive tests, ELISA for IgG, IgA and IgM anticardiolipin antibodies and the dilute Russel's viper venom time (followed by cephalin correction for confirmation) for lupus anticoagulant should be immediately ordered when suspecting the antiphospholipid syndrome in individuals with otherwise unexplained thrombotic or thromboembolic events or recurrent fetal loss. However, if one strongly suspects antiphospholipid thrombosis syndrome clinically and assays for lupus anticoagulants and anticardiolipin antibodies are negative, specific assays for all three idiotypes of phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol and phosphatidylglycerol are available and should be considered. These may clearly be indicated for difficult diagnostic cases of fetal wastage syndrome, and cerebrovascular events, but their significance in other types of thrombosis, particularly venous, remains unclear at present. Since about 65% of patients with antiphospholipid antibodies will fail warfarin therapy (rethrombose), it is important to define this common defect and institute appropriate antithrombotic therapy for appropriate time periods.

Disseminated intravascular coagulation (DIC) is a complex disorder, with pathophysiology being variable and highly dependent upon the triggering event(s), host response(s) and comorbid conditions. As a result of these complicated interactions, the clinical expression and laboratory findings are varied, thereby affecting the specifics of diagnosis and therapeutic approaches. The highly complex and variable pathophysiology of DIC often results in a lack of uniformity in clinical manifestations, a lack of consensus in the specific appropriate laboratory criteria of diagnosis, and a lack of specific therapeutic modalities. Indeed, recommendations for therapy are often difficult because the morbidity and survival is more dependent on the specific cause of DIC and because the generally used specific therapeutic approaches, which include for example heparin, low-molecular-weight-heparin antithrombin concentrate and protein C concentrate, have never been subjected to objective prospective randomized trials, except antithrombin concentrates. An analysis of the complex and varied pathophysiological events in DIC provide objective guidelines and criteria for the clinical diagnosis, the laboratory diagnosis, and the definition of severity. These data compounded by an understanding of complex and varied pathophysiology can be used for objective evaluation of therapeutic responses and results. DIC is an intermediary mechanism of disease usually seen in association with well-defined clinical disorders. The pathophysiology of DIC serves as an intermediary mechanism in many disease processes, which sometimes remain organ specific. This catastrophic syndrome spans all areas of medicine and presents a broad clinical spectrum that is confusing to many. Most physicians consider DIC to be a systemic hemorrhagic syndrome; however, this is only because hemorrhage is evident and often impressive. Less commonly appreciated is the profound microvascular thrombosis and sometimes, large vessel thrombosis. The hemorrhage is often simple to contend with in patients with fulminant DIC, but it is the small- and large-vessel thrombosis, with impairment in blood flow, ischemia, and associated end-organ damage that usually leads to irreversible morbidity and mortality. In conclusion, the pathophysiological mechanisms, clinical, and laboratory manifestations of DIC are complex in part due to interrelationships within the hemostasis system. Only by clearly understanding these extraordinarily complex pathophysiological interrelationships can the clinician and laboratory scientist appreciate the divergent and wide spectrum of often confusing clinical and laboratory findings in patients with DIC. Many therapeutic decisions to be made are controversial and lack validation. Nevertheless, newer antithrombotic agents, and agents which can block, blunt or modify cytokine activity and the activity of vasoactive substances appear to be of value. The complexity and variable degree of clin

In clinical trials, statins (vastatins) reduce cardiovascular disease with cholesterol reduction, but this relationship is unclear. We reasoned that (1) thrombin (IIa) is an underlying mediator of cardiovascular events, (2) IIa mediates cellular events through its primary receptor [protease-activated receptor-1 (PAR-1)], and (3) statins inhibit an isoprenoid-dependent event between PAR-1 activation and tissue factor upregulation leading to IIa generation. In the isoprenoid pathways, statins inhibit mevalonic acid synthesis prior to divergence of the cholesterol and other pathway branches, where the latter produce cell-regulating substances (e.g., ras proteins). Through PAR-1 in platelets and other cells, IIa stimulates G-protein-coupled mechanisms including ras proteins. We hypothesize that statins exhibit antithrombotic properties at the cellular level downregulatating IIa generation and that statins may constitute a novel class of antithrombotics.

Low-molecular-weight heparins (LMWHs), like unfractionated heparin (UFH), exert their action primarily by accelerating the interaction between antithrombin (AT) and thrombin. At the levels of aXa activity that are attained in human pharmacology, it does not cause significant (>15%) inhibition of the clotting system. The essential differences between LMWHs and UFH are: (a) LMWHs attain higher plasma concentrations after subcutaneous injection (high bioavailability), and (b) in contrast to LMWHs, UFH contains very large heparin molecules with a putative hemorrhagic action. The reputedly higher aXa activity of LMWH can be shown to be largely due to the absence of Ca(2+) using the current laboratory methods to estimate this activity. Via this artifact the apparently high aXa activity of LMWHs is correlated but not related to their favorable pharmacokinetic properties. Consequently dosage guidelines for the use of different LMWHs cannot be based upon their aXa activity. Until better laboratory methods are available, clinical results are the only reliable guideline to heparin dosage.

Fibrinogen is a central protein in blood coagulation. A functioning circulation system requires a precise balance between fibrin formation and removal, i.e. between the interaction of fibrin(ogen) with thrombogenic and fibrinolytic components of the blood. Fibrinogen and fibrin have also significant roles in wound healing, in tumor growth and metastasis as well as in defense mechanisms. All functions and interactions are mediated by specific structural elements of the molecule. Already in healthy individuals fibrinogen occurs in over a million nonidentical forms due to posttranslational modifications and genetic polymorphism. The various forms may show considerable differences in their functional properties. Alterations in distributions among preexisting forms as well as additional forms have been observed to accompany many types of disease. Furthermore, certain forms have been correlated with an increased risk to acquire disease. Monitoring the levels of various molecular forms is expected to be of considerable diagnostic and prognostic value in many types of disease.

A prospective open-labeled clinical study was carried out to compare the safety of dextran 70 and low molecular weight heparin (dalteparin; DD group) versus dextran 70 alone (D group) in patients subjected to elective hip replacement surgery. Dalteparin, 5,000 IU/day and dextran 70, 500 ml during surgery and on the first postoperative day were administered to 214 patients. Dextran 70 alone was infused in 44 patients, 500 ml during surgery and on the 1st, 3rd and 5th postoperative day. Mean total blood loss during the operation and until the 2nd postoperative day was 1,708 ml in the DD group and 1,712 ml in the D group (p = 0.79). During the 1st postoperative week, no group differences were found in the relative number of patients that received packed red blood cells (p = 0.95), the amount of transfused packed red blood cells (p = 1.0) and changes in hemoglobin concentrations (p = 0.69). The present results suggest that dextran 70 and dalteparin can be combined in recommended doses without significantly increasing perioperative bleeding in patients undergoing hip replacement surgery. Bone traumatization and insufficient plugging of surgical traumatized bone surfaces with bone cement favor bleeding. Further well-designed studies are needed to evaluate the safety and efficacy of this regimen.

We examined and compared the effects of aspirin (ASA), ticlopidine (TP) and cilostazol (CS) on bleeding time (BT) in 10 healthy adult male subjects using a newly developed quantitative bleeding time (QBT) test apparatus capable of simultaneously measuring total blood loss (Tv), maximum bleeding rate (Rmax), and bleeding pattern in addition to BT. All 3 drugs inhibited platelet aggregation response to ADP, collagen, epinephrine and arachidonic acid (p < 0.05), but not to ristocetin. Following oral administration of ASA (330 mg/day) or TP (300 mg/day) for 3 days, BT was significantly prolonged (mean BT increased from 359.3 to 646.0 s, p < 0.001, and from 323.3 to 528. 7 s, p < 0.01, respectively) and Tv was significantly increased (from 14.5 to 30.2 microl, p < 0.05, and from 12.5 to 19.2 microl, p < 0.01, respectively). Aspirin also increased Rmax (from 0.118 to 0. 159 microl/s, p < 0.05). The prolonged bleeding patterns after administration of ASA and TP were both type III, which has been reported to be less likely to lead to bleeding accidents. In contrast, none of these QBT parameters were altered by CS administration.