Haemostasis最新文献

A pilot study was performed to compare the thromboprophylactic effect of danaparoid, enoxaparin and dalteparin in patients with hip fracture. The study was a prospective, randomised assessor-blind, four-centre trial. Prophylaxis was given for 9-11 days, whereafter bilateral phlebography was performed. A total of 197 patients were randomised. There were no statistically significant differences in the frequency of deep vein thrombosis, in blood loss or bleeding complications between the three prophylaxis groups. In conclusion, this moderately sized study revealed no statistically significant difference in efficacy or safety between danaparoid, enoxaparin and dalteparin in patients undergoing hip fracture surgery.

The aim of this prospective study was to examine the role of coagulation factor XIII (FXIII) in relation to disease activity in inflammatory bowel disease (IBD) and in giant cell arteritis. Plasma FXIII activity was studied during active and inactive disease in newly diagnosed patients with Crohn's disease (CD; n = 20), ulcerative colitis (UC; n = 18) and giant cell arteritis (GCA; n = 19), in 3-month intervals (median follow-up 12 months). FXIII was also measured in two noninflammatory control groups, age and sex matched for IBD (n = 25) and GCA (n = 26). FXIII activity was significantly lower in active CD or UC than in active GCA or the noninflammatory controls. Both in CD and UC, FXIII activity correlated inversely with indices of clinical disease activity, the erythrocyte sedimentation rate, fibrinogen and C-reactive protein levels. Low FXIII activity is a characteristic feature of active IBD, and serial measurements may be useful to assess IBD activity.

Thrombin is a serine protease which is generated from its precursor prothrombin by the activation of the blood coagulation cascade. Thrombin converts fibrinogen to fibrin, activates platelets and several coagulation factors, and plays a central role in thrombosis and hemostasis by regulating platelet aggregation and blood coagulation. Here, we show that thrombn enhanced vascular endothelial growth factor (VEGF) production in a dose- and time-dependent manner in the supernatant of cultured PC-12 cells, as determined by enzyme-linked immunosorbent assay (ELISA). Thrombin receptor agonist peptide (SFLLRNPNDKYEPF, TRAP) exerted an effect similar to thrombin on VEGF production. Thrombin-induced VEGF production was significantly attenuated by recombinant human thrombomodulin (rTM) and its minimal functional domain E456. Furthermore, the antioxidant N-acetyl-L-cysteine (NAC) markedly inhibited thrombin-induced VEGF production. Thus, rTM and NAC apparently inhibited the effect of thrombin on VEGF production in neuronal cells.

The aim of the study was to evaluate any correlation between the circulating oestrogenic hormone 17beta-oestradiol and haemostatic factors in healthy postmenopausal women. In keeping with this objective, the correlations were evaluated irrespective of whether the source of the hormone was purely endogenous or exogenous as well. Accordingly, a univariate correlation adjusted for age, body mass index, and duration of menopause was determined in 42 healthy postmenopausal women aged 47-78 years, 19 of whom were self-reported users of hormone replacement therapy. The rest were self- reported never users. Serum 17beta-oestradiol exhibited a direct correlation with endogenous thrombin potential extrinsic pathway (R = 0.42, p = 0.01) and prothrombin fragments 1 and 2 (R = 0.37, p = 0.03) and an inverse correlation with antithrombin III (R = -0.36, p = 0.03) and alpha(2)-antiplasmin (R = -0.45, p = 0.005). The observations suggest an association of this hormone with net thrombin generation on the one hand and improved fibrinolysis on the other.

Clinical observations have indicated the frequent development of thrombotic complications during diabetic ketoacidosis (DKA). This study aimed to examine whether haemostatic changes that could lead to a thrombotic tendency occur during ketoacidosis. Plasma levels of in vivo haemostatic markers reflecting activation degrees of the coagulation system, fibrinolytic system, platelets and endothelium were assayed in 34 patients with DKA, both at diagnosis and 1 week after recovery. We found coagulation system and platelet activation and endothelial injury/activation in the patients at diagnosis of DKA. Although significant improvements were observed after recovery, only platelet activity was completely normalized. Fibrinolytic activity was also increased, both at diagnosis and after recovery, compared to the control group. However, although coagulation activity was prominently increased at diagnosis compared to the recovery period, there was no change in fibrinolytic activity in the same periods; on the contrary, the fibrinolytic capacity of the endothelium was diminished at diagnosis of DKA compared to the recovery period, suggesting the presence of relative hypofibrinolysis during DKA. Indications for a role of hyperglycaemia in the emergence of haemostatic disturbances during DKA were observed.

Platelet activation results in shape change, release of granule contents, aggregation and clot retraction. An intense intracellular 'machinery' is engaged to achieve these functions. Thrombin is one of the most important agonists for platelet recruitment and aggregation which is mediated by the binding of fibrinogen to its adhesive receptor: the glycoprotein (GP) IIb/IIIa complex or integrin alphaIIbbeta(3). The numerous biological processes consecutive to thrombin binding to platelet membrane are mainly controlled by phosphorylation mechanisms organized into signalling pathways. Schematically, the phospholipase Cbeta pathway activated by G protein coupled to the seven transmembrane thrombin receptors, provides the first intracellular relay and would generate regulators such as protein kinase C, phosphorylated pleckstrin but also modifications of the intracellular domain of beta(3). This inside-out signalling would lead to some changes in the extracellular domain of GPIIb/IIIa increasing access of fibrinogen to the receptor. Ligand interaction with GPIIb/IIIa induced reorganization of the cytoskeleton and would mediate the outside-in signals which involve a series of intracellular events including tyrosine kinases, phosphatidylinositol 3 kinases, MAP kinases and phosphatases. Some of these pathways and/or signalling metabolites could be associated to some well-characterized platelet functions: cortactin phosphorylation is involved in platelet shape change, phosphatidylinositol 3 kinase (p85) in the stabilisation of platelet aggregates and MAP kinase (p44) in postaggregation events. But in fact the sequence of events which has been described has to be viewed as integrated networks. At least three biochemical processes govern the highly integrated organization to send just the appropriate quanta of signal for a specific need: the reorganisation of the cytoskeleton following the binding of fibrinogen to alphaIIbbeta(3), the structure of the signal transducers that contain SH2, SH3, and PH domains leading to the formation of macromolecules of signalling and the crosstalk phenomena between the different pathways. Elucidating the mechanisms of such networks becomes an increasingly exciting project.

After 35 years of research, a physiological regulator of platelet production has been identified and the recombinant protein is available. With the discovery of thrombopoietin (TPO), its potential use in a wide variety of clinical megakaryocytic and platelet disorders has been expected and clinical trials have been undertaken. To date, the reported encouraging pre-clinical studies indicate that, as with erythropoietin or G-CSF, minimal toxicity can be expected. A potential limiting side-effect of TPO could be the induction of thrombosis. Nevertheless, it is too early to know whether this cytokine will be of major therapeutic importance for patients with life-threatening thrombocytopenia, such as patients undergoing bone marrow transplantation or subjected to a high dose of chemotherapy. Several experimental and clinical studies are still needed to determine the efficacy of TPO in the prevention or the amelioration of bleeding, which is the ultimate goal for the appropriate use of cytokines with haemostatic benefit. Basic and clinical studies on regulators of megakaryocytopoiesis have rapidly progressed. Now, there is no doubt that some of these regulators are effective in correcting haematopoietic disorders of various aetiologies. Studies on negative regulators not only are important to understand the regulation of megakaryocytopoiesis in normal and pathological states but also have a potential clinical application. Some of these regulators have been shown to be effective in the treatment of essential thrombocythaemia and other myeloproliferative disorders. Platelet factor 4 (PF4) and some other chemokines are also capable of protecting progenitor cells from the cytotoxicity of chemotherapeutic drugs. However, detailed investigations are still required to determine the precise mechanism(s) of action of these regulators and to establish the optimal clinical protocols of negative regulators alone or in association with positive regulators for the treatment of various haematological diseases and cancer.

Collagen is a major component of extracellular matrix and a wide variety of types exist. Cells recognise collagen in different ways depending on sequence and structure. They can recognise predominantly primary sequence, they may require triple-helical structure or they can require fibrillar structures. Since collagens are major constituents of the subendothelium that determine the thrombogenicity of the injured or pathological vessel wall, a major role is induction of platelet activation and aggregation as the start of repair processes. Platelets have at least two direct and one indirect (via von Willebrand factor) receptors for collagen, and collagen has specific recognition motifs for these receptors. These receptors and recognition motifs are under intensive investigation in the search for possible methods to control platelet activation in vivo. A wide range of proteins has been identified and, in part, characterised from both haematophageous insects and invertebrates but also from snake venoms that inhibit platelet activation by collagen or induce platelet activation via collagen receptors on platelets. These will provide model systems to test the effect of inhibition of specific collagen-platelet receptor interactions for both effectiveness as well as for side effects and should provide assay systems for the development of small molecule inhibitors. Since platelet inhibitors for long-term prophylaxis of cardiovascular diseases are still in clinical trials there are many unanswered questions about long-term effects both positive and negative. The major problem which still has to be definitively solved about these alternative approaches to inhibition of platelet activation is whether they will show advantages in terms of dose-response curves while offering decreased risks of bleeding problems. Preliminary studies would seem to suggest that this is indeed the case.