Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.69 (APC)
 16,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Platelet-dependent thrombosis and subsequent embolization are major causes of cerebral ischaemia. Beside aspirin which irreversibly blocks platelet cyclo-oxygenase, several other substances interfere in different platelet metabolic pathways and block platelet adhesion and aggregation. We found in an experimental model using non-human primates that a specific peptide inhibitor blocking GP IIb/IIIa platelet receptor which binds fibrinogen completely, prevents the retention of embolized platelet aggregates in the cerebral circulation. As thrombin may play a key role for platelet activation in vivo leech-derived hirudin, a direct thrombin inhibitor as well as activated protein C which limits thrombin production and also prevents platelet dependent thrombus formation very effective. We demonstrated in the same non-human primate model of platelet embolization that the amount of retention of platelet emboli in the vascular bed depends on the nature of the vasculature. For example, platelet emboli were cleared very quickly from brain microcirculation, whereas platelet embolization into the lower limb via the femoral artery caused a significantly longer retention of the embolized material. Such specific mechanisms may be caused by different levels of local vasodilators as PGI2 or EDRF.
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PMID:Platelet thromboembolism. 801 31

The established antithrombotic agents are effective but they have limitations which have provided opportunities for the development of new antithrombotic compounds. Of these new agents, the antithrombin III-independent thrombin inhibitors and the platelet GPIIb/IIIa receptor antagonists are the most advanced in their development. Other new antithrombotic agents include the antithrombin III-independent factor Xa inhibitors, activated protein C, soluble thrombomodulin and tissue factor pathway inhibitor. Of the GPIIb/IIIa antagonists, the humanized 7E3 antibody and integrin have been evaluated in phase III studies. The 7E3 antibody was effective in preventing both short-term and longer-term complications of coronary angioplasty. The antithrombin III-independent thrombin inhibitors hirudin and hirulog have also been evaluated in phase III studies. The studies with hirudin as an adjuvant to coronary thrombolysis had to be terminated and restarted at lower dosages because of an unacceptable incidence at intracranial hemorrhage and the study with hirulog produced equivocal results.
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PMID:New antithrombotics for the treatment of acute and chronic arterial ischemia. 954 19

Snake venom toxins are now regularly used in the coagulation laboratory for assaying haemostatic parameters and as coagulation reagents. Snake venom thrombin-like enzymes (SVTLE) are used for fibrinogen and fibrinogen breakdown product assay as well as detecting dysfibrinogenaemias. Significantly, because SVTLE are not inhibited by heparin, they can be used for defibrinating samples that contain the anticoagulant before assay of haemostatic variables. Prothrombin activators are found in many snake venoms and are used in prothrombin assays, for studying dysprothrombinaemias and preparing meizothrombin and non-enzymic prothrombin. Russell's viper (Daboia russelli) venom (RVV) contains a number of compounds useful in the assay of factors V, VII, X, platelet factor 3 and lupus anticoagulants. Activators from the taipan, Australian brown snake and saw-scaled viper have been used to assay lupus anticoagulants. Protein C and activated protein C resistance can be measured by means of RVV and Protac, a fast acting inhibitor from Southern copperhead snake venom and von Willebrand factor can be studied with Botrocetin from Bothrops jararaca venom. Finally, phospholipase A2 enzymes and the disintegrins, a family of Arg-Gly-Asp (RGD)-containing proteins found in snake venoms, show great potential for the study of haemostasis including, notably, platelet glycoprotein receptors GPIIb/IIIa and Ib.
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PMID:Use of snake venom fractions in the coagulation laboratory. 971 87

Snake venoms are complex mixtures containing many different biologically active proteins and peptides. A number of these proteins interact with components of the human hemostatic system. This review is focused on those venom constituents which affect the blood coagulation pathway, endothelial cells, and platelets. Only highly purified and well characterized snake venom proteins will be discussed in this review. Hemostatically active components are distributed widely in the venom of many different snake species, particularly from pit viper, viper and elapid venoms. The venom components can be grouped into a number of different categories depending on their hemostatic action. The following groups are discussed in this review: (i) enzymes that clot fibrinogen; (ii) enzymes that degrade fibrin(ogen); (iii) plasminogen activators; (iv) prothrombin activators; (v) factor V activators; (vi) factor X activators; (vii) anticoagulant activities including inhibitors of prothrombinase complex formation, inhibitors of thrombin, phospholipases, and protein C activators; (viii) enzymes with hemorrhagic activity; (ix) enzymes that degrade plasma serine proteinase inhibitors; (x) platelet aggregation inducers including direct acting enzymes, direct acting non-enzymatic components, and agents that require a cofactor; (xi) platelet aggregation inhibitors including: alpha-fibrinogenases, 5'-nucleotidases, phospholipases, and disintegrins. Although many snake venoms contain a number of hemostatically active components, it is safe to say that no single venom contains all the hemostatically active components described here. Several venom enzymes have been used clinically as anticoagulants and other venom components are being used in pre-clinical research to examine their possible therapeutic potential. The disintegrins are an interesting group of peptides that contain a cell adhesion recognition motif, Arg-Gly-Asp (RGD), in the carboxy-terminal half of their amino acid sequence. These agents act as fibrinogen receptor (integrin GPIIb/IIIa) antagonists. Since this integrin is believed to serve as the final common pathway leading to the formation of platelet-platelet bridges and platelet aggregation, blockage of this integrin leads to inhibition of platelet aggregation regardless of the stimulating agent. Clinical trials suggest that platelet GPIIb/IIIa blockade is an effective therapy for the thrombotic events and restenosis frequently accompanying cardiovascular and cerebrovascular disease. Therefore, because of their clinical poten tial, a large number of disintegrins have been isolated and characterized.
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PMID:Snake venoms and the hemostatic system. 983 63

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.
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PMID:On the coagulation of platelet-rich plasma. Physiological mechanism and pharmacological consequences. 1049 34

We have investigated beta2-glycoprotein I (beta2GPI) binding to platelet-derived microparticles (PMP) and its effect on GPIIb/IIIa. PMP were isolated from washed human platelets after stimulation with A23187, and analyzed by surface plasmon resonance spectroscopy. Beta2GPI as well as activated protein C (APC) or annexin V bound to PMP-coated sensorchips, demonstrating exposure of anionic phospholipids on immobilized PMP. Beta2GPI binding was impaired by calcium and occurred in a concentration-dependent manner with apparent k(on) = 2.6 x 10(4) M(-1) s(-1) and k(off) = 4.4 x 10(-3) s(-1), corresponding to a KD value of 1.7 x 10(-7) M. When analyzed by flow cytometry, the binding of certain mAbs specific for GPIIb and/or GPIIIa was reduced in the presence of beta2GPI but not of APC or annexin V, whereas the binding of anti-GPIb or anti-P-selectin mAbs, or of soluble fibrinogen remained unchanged. These results suggest a broad but specific influence of beta2GPI on GPIIb/IIIa immunoreactivity, and indicate that beta2GPI may act as a modulator of GPIIb/IIIa-dependent functions of PMP.
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PMID:Beta2-glycoprotein I binding to platelet microparticle membrane specifically reduces immunoreactivity of glycoproteins IIb/IIIa. 1124 54

The role of genetic susceptibility to coronary artery disease (CAD) seems to be quite important in young patients. In the last years the attention has been focused on polymorphisms influencing some biological functions (coagulation and fibrinolysis, platelets, vascular function, lipid metabolism, inflammation). The study of prothrombotic polymorphisms has kindled a deep interest. The role of atherosclerosis and thrombosis is different in the different ages. In all the studies we examined, the polymorphism G20210A in the prothrombin gene was associated with an increased risk of acute myocardial infarction (AMI) in young people, especially when other risk factors were present. Contradictory results have been found in the studies on Factor V Leiden: according to many authors the activated protein C resistance (APCR) is associated with an increased risk of AMI only in smokers, above all if women. On the other hand, some polymorphisms of the Factor VII gene seem to be protective. Young AMI could be also caused by a reduction of the fibrinolytic activity, as it was found when the allele 4G in the promoter of plasminogen activator inhibitor (PAI) gene is present. The attention has also been focused on the effects of variations in genes that influence platelet functions. According to a metanalysis of studies published up to 1999, there is no association between the polymorphism PlA1/A2 of the GP IIIa gene and young AMI, whereas there is doubt about the role of the polymorphism in the GP IIb e GP Ib genes. Moreover, it seems to be present an association with the polymorphisms in the thrombopoietin gene (C4830A and A5713G). Also the role of some genes coding for proteins influencing the vascular functions has been valued. Few studies were performed on genetics of the renin-angiotensin-aldosterone system and the results are insufficient and contradictory, such as those about the association between the polymorphism G894T in the eNOS gene or the polymorphism C677T in the MTHFR gene and young AMI. Genes coding for proteins involved in the lipid metabolism have been closely examined. Many polymorphisms were discovered in the Apo B gene: the variant C-516T was found to be associated with increased LDL levels, whereas the results about the association between this and other polymorphisms in the same gene (I/D of LAL sequence, PvuII, MspI, Asp4311Ser) and young AMI are discordant. On the other hand, the variant e4 of the ApoE gene was associated with an increased risk of AMI at young age in many works. In the last years, a particular interest has kindled the study of the relationship between inflammation, atherosclerosis and CAD. Even if the studies performed are few, it was found an association between young AMI and polymorphism C-260T in the CD14 gene, between coronarics atherosclerosis and polymorphism A516C in the E Selectin gene or polymorphisms Leu125Val and Ser563Asn in the PECAM1 gene.
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PMID:Genetic risk factors in myocardial infarction at young age. 1528 79

Snake venom toxins affecting haemostasis have facilitated extensively the routine assays of haemostatic parameters in the coagulation laboratory. Snake venom thrombin-like enzymes (SVTLE) are used for fibrinogen/fibrinogen breakdown product assay and for the detection of fibrinogen dysfunction. SVTLE are not inhibited by heparin and can thus can be used for assaying antithrombin III and other haemostatic variables in heparin-containing samples. Snake venoms are a rich source of prothrombin activators and these are utilised in prothrombin assays, for studying dysprothrombinaemias and for preparing meizothrombin and non-enzymic forms of prothrombin. Russell's viper (Daboia russelli) venom (RVV) contains toxins which have been used to assay blood clotting factors V, VII, X, platelet factor 3 and, importantly, lupus anticoagulants (LA). Other prothrombin activators (from the taipan, Australian brown snake and saw-scaled viper) have now been used to assay LA. Protein C and activated protein C resistance can be measured by means of RVV and Protac, a fast acting inhibitor from Southern copperhead snake venom and von Willebrand factor can be studied with botrocetin from Bothrops jararaca venom. The disintegrins, a large family of Arg-Gly-Asp (RGD)-containing snake venom proteins, show potential for studying platelet glycoprotein receptors, notably, GPIIb/IIIa and Ib. Snake venom toxins affecting haemostasis are also used in the therapeutic setting: Ancrod (from the Malayan pit viper, Calloselasma rhodostoma), in particular, has been used as an anticoagulant to achieve 'therapeutic defibrination'. Other snake venom proteins show promise in the treatment of a range of haemostatic disorders.
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PMID:Practical applications of snake venom toxins in haemostasis. 1592 82

We prospectively assessed whether thrombophilia and hypofibrinolysis, amplified by thrombophilic hormone replacement therapy (HRT), were associated with retinal vein occlusion (RVO). We studied 44 cases (18 men, 26 women), > or = 3 months after RVO, 42 with central RVO, 2 with branch RVO, in the consecutive order of their referral by 2 community-based ophthalmologists. PCR and serologic coagulation assays were compared to 83 and 40 healthy adult normal controls, respectively. The 4G allele frequency of the plasminogen activator inhibitor-1 (PAI-1) gene, associated with hypofibrinolysis, was 56 of 88 (64%) in cases vs 79 of 166 (48%) in controls, X(2) = 5.95, p = .015. The PAI-1 gene product, plasminogen activator inhibitor activity (PAI-Fx), was higher in cases than controls (age-race-sex- adjusted mean 12.2 U/mL vs 6.3, p = .013). By stepwise logistic regression, the PAI-1 gene 4G allele was associated with RVO, odds ratio 1.94, 95% CI 1.12-3.34, p = .018. Thrombophilic resistance to activated protein C (RAPC) was present in 6 of 32 (19%) of cases vs 0 of 40 (0%) controls, Fisher's p [p(f)] = .006. Thrombophilic high factor VIII (> 150%) was present in 3 of 30 (10%) cases vs 0 of 40 (0%) controls, p = .041, p(f) = .07. Comparing 23 RVO cases < or = age 55 and controls < or = age 55 (n = 44 for PCR, n = 40 for serologic measures), RAPC was present in 17% of cases vs 0% controls (p(f) = .026), high Factor VIII in 17% vs 0% (p(f) = .026), heterozygosity for the G1691A Factor V Leiden mutation in 13% vs 2% (p(f) = 0.11), and the 4G allele frequency of the PAI-1 gene 74% vs 39% (p = .0001). PAI-Fx was higher in cases than controls (age-race-sex adjusted mean 12.7 U/mL vs 6.7, p = .016). The case-control odds ratio for the PAI-1 4G allele was 5.54, 95% CI = 1.86-16.7, p = .002. Of the 26 women, 9 (35%) took HRT; 4 of the 9 had PAI-1 gene 4G4G homozygosity, 2 had thrombophilic high anticardiolipin antibody (IgG), 1 was heterozygous for the G1691A Factor V Leiden mutation, and 2 were heterozygous for the thrombophilic PL A1/A2 mutation of the platelet glycoprotein IIb/IIIa gene. Associations between heritable coagulation disorders and RVO, most marked in cases < or = age 55, and often amplified in women by thrombophilic HRT, are, speculatively, causal.
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PMID:Associations of thrombophilia, hypofibrinolysis, and retinal vein occlusion. 1624 63

The existence of an association between idiopathic intracranial hypertension (IIH) and coagulation disorders in men was assessed prospectively. Microthrombi, associated with thrombophilia-hypofibrinolysis, occlude arachnoid sinus villi, thus reducing resorption of cerebrospinal fluid, leading to IIH. Ten consecutively referred men with IIH, nine whites, one African American, median age 36 years, were 2 to 1 matched by age and race by healthy male controls. Polymerase chain reaction assays were done for four thrombophilic and one hypofibrinolytic gene mutations: G1691A factor V Leiden, G20210A prothrombin, C677T MTHFR, platelet glycoprotein IIb/IIIa (PL A1/A2), and 4G/5G polymorphism of the plasminogen activator inhibitor (PAI-1) gene promoter. Coagulation measures in plasma included dilute Russel's viper venom time (dRVVT), activated partial thromboplastin time (aPTT), the lupus anticoagulant, factor VIII, factor XI, plasminogen activator inhibitor activity (PAI-Fx), protein C antigenic, protein S total (antigenic), protein S free (antigenic), antithrombin III (functional), and resistance to activated protein C (RAPC). Tests performed on serum included anticardiolipin antibodies, homocysteine, and Lp(a). The body mass index was 40 kg/m(2) or greater (extremely obese) in two men, 30 to 40 kg/m(2) (obese) in three, and was 25 to 30 kg/m(2) in five (overweight). Cases differed from controls for inherited 4G4G homozygosity of the PAI-1 gene, four of 10 (40%) vs. one of 20 (5%), Fisher's p [p(f)]= .031, and for high levels (>21.1 U/mL) of the hypofibrinolytic PAI-1 gene product, PAI-Fx, 5 of 10 (50%) vs. one of 18 (6%), p(f) = .013. Thrombophilic factor VIII was high (> or = 150%) in three of 10 (30%) cases vs. zero of 16 (0%) controls, p(f)=. 046. The thrombophilic lupus anticoagulant was present in two of 10 (20%) cases vs. zero of 32 (0%) controls, p(f) = .052. Heritable hypofibrinolysis and heritable and acquired thrombophilia appear, speculatively, to be treatable etiologies of IIH in men. Understanding contributions of hypofibrinolysis and thrombophilia to the development of IIH should facilitate development of novel new approaches to treat this often-disabling neurologic disorder.
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PMID:Idiopathic intracranial hypertension: associations with thrombophilia and hypofibrinolysis in men. 1624 70


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