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

Protein S is a vitamin K-dependent nonenzymatic coagulation factor involved in the regulation of activated protein C (aPC). In this study, we report an aPC-independent anticoagulant function of protein S in plasma under flow conditions. Plasma, anticoagulated with low-molecular-weight heparin allowing tissue factor-dependent prothrombin activation, was perfused at a wall shear rate of 100 s-1 over tissue factor containing matrices of stimulated endothelial cells placed in a perfusion chamber. Fractions were collected in time at the outlet and prothrombin activation was determined by measuring the activation fragment F1+2 of prothrombin. In normal plasma, a time-dependent prothrombin activation was detected by the generation of fragment1+2. Prothrombin activation had ceased after 12 minutes perfusion, independent of the amount of tissue factor present in the matrix. Depletion of protein S from plasma or inhibition of protein S in plasma by monoclonal antibodies induced a 5- to 25-fold increase of prothrombin activation on the procoagulant endothelial cell matrix. A prolonged prothrombin activation was detected in protein S-depleted plasma up to 20 minutes after onset of the thrombin generation. The increased prothrombin activation in protein S-depleted plasma could not be explained by the absence of the cofactor function of protein S for aPC because depletion of protein C from plasma did not result in increased prothrombin activation. These data provide further evidence for a strong anticoagulant function of protein S in plasma independent from activated protein C.
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PMID:Increased prothrombin activation in protein S-deficient plasma under flow conditions on endothelial cell matrix: an independent anticoagulant function of protein S in plasma. 770 88

To investigate the effect of warfarin treatment on the early phase of tissue factor-induced coagulation, we measured plasma-activated factor VII (factor VIIa) levels by a direct fluorogenic assay in 74 cardiovascular disease patients on long-term oral anticoagulation. We divided the patients into three groups based on the international normalized ratio (INR). In the patients with INR ranges of < 1.7 and 1.7 to 2.5, factor VIIa levels were 42% and 61% lower, respectively, than in age- and sex-matched controls. Factor VII coagulant activity (factor VIIc), factor VII antigen (factor VIIag), protein C, and factor X levels were also reduced to a similar extent in both groups. However, in patients with an INR > 2.5, the factor VIIa level was not decreased compared with that at an INR of 1.7 to 2.5, although the factor VIIc, factor VIIag, factor X, and protein C levels were all decreased further. Although the precise relation between the reduction of factor VIIa levels and the increase of INR requires appropriately designed long-term clinical trials, our data suggest that an INR range of 1.7 to 2.5 is sufficient for the suppression of factor VIIa. During the long-term follow-up of three patients with congenital antithrombin III or protein C deficiency, the factor VIIa level was more responsive to changes in the warfarin dose than the INR, and there were generally no corresponding changes of the thrombin-antithrombin III complex (TAT) level. However, one patient showed a transient marked increase of factor VIIa during the discontinuation of warfarin that was accompanied by an increase in TAT. Based on these findings, factor VIIa could be useful for monitoring both hypercoagulable and hypocoagulable states.
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PMID:Suppression of plasma-activated factor VII levels by warfarin therapy. 774 32

This review has stressed the common hereditary and acquired blood protein defects associated with thrombosis. The most common of the hereditary defects appear to be antithrombin, protein C, and protein S deficiency, and the most common acquired defects are anticardiolipin antibodies and the lupus anticoagulant. Therefore, these are the defects which should first be searched for in an individual with unexplained thrombosis. If these more common defects are not found, the rarer defects, including HC-II, plasminogen, or TPA deficiency, dysfibrinogenemia, elevated PAI-1, or heterozygous homocystinemia should be looked for. The incidence of activated protein C co-factor deficiency (APC resistance) is not yet clear but may also represent a common defect. PAI-1 defects may, with time, be shown to be common. Finding these defects has important implications for therapy for the individual patient and for the institution of family studies to identify, inform, and possibly treat others at risk. It is expected that as knowledge of hemostasis expands, more hereditary and acquired defects, such as elevated lipoprotein(a) or defects of extrinsic (tissue factor) pathway inhibitor (EPI, TFPI), may be associated with enhanced risks for thrombosis.
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PMID:Blood protein defects associated with thrombosis. Laboratory assessment. 778 Dec 75

The baboon model of E. coli sepsis illustrates three concepts with respect to the host response and vascular endothelium. First, the endothelium is the primary target. E. coli sepsis is an acute inflammatory disease of the vascular endothelium. Second, the endothelium is not a passive target. Initially it regulates both the inflammatory and coagulopathic aspects of E. coli sepsis through membrane associated regulatory receptor/plasma protein assemblies including protein C/thrombomodulin, activated protein C/protein S, C4bBP/protein S, tissue factor pathway inhibitor/Xa, antithrombin III/glycosaminoglycans. Third, when overridden by inflammatory events, the endothelium can change its anticoagulant phenotype and mount a massive procoagulant fibrinolytic counter-attack on its luminal side through the expression of tissue factor and release of tissue plasminogen activator. Fourth, again when overridden by inflammatory events, the endothelium can change its antioxidant phenotype and produce a "distal" tissue hypoxia on its abluminal side through induction of free radical generation and peroxidation of mitochondrial lipid membranes of those tissues with high metabolic rates. It has become increasingly clear that the so-called anticoagulant systems which act on the proximal factors of the clotting cascade (protein C, TFPI, AT-III, PGI2) also attenuate the amplification of the inflammatory response. Aspects of the mechanism by which this occurs are coming to light. This includes the attenuation of Il-6 response by TFPI and the attenuation of the complement effects by C4bBP/PS. The specifics of these observations in the E. coli sepsis model will be reviewed.
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PMID:Studies on the inflammatory-coagulant axis in the baboon response to E. coli: regulatory roles of proteins C, S, C4bBP and of inhibitors of tissue factor. 783 58

Antiphospholipid antibodies are a diverse group of immunoglobulins initially thought to have specificity to phospholipid epitopes. It is apparent that autoimmune anticardiolipin antibodies require a serum cofactor beta-2-glycoprotein I (beta 2GPI) for their binding to phospholipids. Lupus anticoagulant also may bind to phospholipids by beta 2GPI or by prothrombin. The description of binding to protein-phospholipid epitopes may explain several perplexing features of these antibodies both in vitro and in vivo. Antiphospholipid antibodies have a well-established association with clinical disease--in particular thrombosis, thrombocytopenia and recurrent fetal loss. The mechanism of the predisposition to thrombosis seen with these antibodies is poorly understood. It has been suggested that they may cause endothelial dysfunction by causing increased tissue factor expression, by inhibiting prostacyclin secretion or by inhibiting fibrinolysis. Various platelet-activating activities have also been described. The evidence that antiphospholipid antibodies promote thrombosis by effects on endothelium or platelets is inconclusive. Inhibition of protein C activation, or of activated protein C action, has been demonstrated in vitro. A poor correlation between thrombosis in vivo and these inhibitory effects has been found. Beta-2-glycoprotein I has been identified as a cofactor for binding to phospholipid by thrombogenic anticardiolipin antibodies. That beta 2GPI may be a natural anticoagulant of importance remains to be proved. Inhibition by antiphospholipid antibodies of this anticoagulant function could explain the propensity to thrombosis seen in association with these antibodies.
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PMID:Antiphospholipid antibodies and thrombosis. 784

Hepatic venocclusive disease causes considerable morbidity and mortality following bone marrow transplantation. There are two hypotheses regarding the aetiology of this syndrome; firstly that changes in plasma coagulation factors and natural anticoagulants lead to a prothrombotic state and secondly that endothelial cell activation stimulates intravascular deposition of fibrin. We have investigated these mechanisms by measuring the changes in proteins C and S and factors VII and X in the post transplant period and by using the plasma concentration of factor VIIa as an in vivo marker of potential endothelial cell tissue factor expression. Protein C fell in both allograft and autograft patients but more so in the allografts. Similar results were found for factors VII and X. These changes were predominantly due to hepatic dysfunction induced by the chemo-radiotherapy. Factor VIIa levels were unchanged in both the allograft and autograft patients. We conclude that there is no convincing evidence for a procoagulant state following BMT as there are both anticoagulant and procoagulant changes. The absence of any changes in factor VIIa levels suggests that tissue factor was not exposed to the general circulation following BMT but does not exclude focal expression at the sites of thrombosis.
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PMID:Factor VIIa and other haemostatic variables following bone marrow transplantation. 797 71

Activated protein C reduces thrombin generation by inactivating factors V and VIII in the presence of protein S. This prompted us to develop an assay which would allow specific exploration of this reaction. The total amount of thrombin formed in plasma after activation by tissue factor and phospholipids was reduced by adding thrombomodulin. This addition allowed protein C to be activated by endogenous thrombin. The inhibition of thrombin generation (ITG) due to protein C activation could be measured by comparing thrombin formation in the presence and in the absence of thrombomodulin. ITG increased with both protein C and protein S concentrations. Normal values of ITG expressed as a percentage were between 40 and 65% and were not influenced by age or sex. ITG increased in patients under heparin therapy, decreased in patients under oral anticoagulant therapy and was decreased in women using oral contraceptives. This method could be used for screening patients for protein C and protein S deficiencies.
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PMID:A new assay based on thrombin generation inhibition to detect both protein C and protein S deficiencies in plasma. 802 98

This review has stressed the common hereditary and acquired blood protein defects associated with thrombosis. The most common of the hereditary defects appear to be antithrombin, protein C, and protein S deficiency and the most common acquired defects are anticardiolipin antibodies and the lupus anticoagulant. Therefore these are the defects that should first be looked for in an individual with unexplained thrombosis. If these more common defects are not found, then the rarer defects, including heparin cofactor II, plasminogen or tissue plasminogen activator deficiency, dysfibrinogenemia, or elevated PAI-1 should next be sought. The importance of finding these defects has significant implications for therapy of the individual patient and for institution of family studies to identify, inform, and possibly treat others at risk. It is expected that as knowledge of hemostasis expands, more hereditary and acquired defects, such as elevated lipoprotein(a) or defects of extrinsic (tissue factor) pathway inhibitor may be associated with enhanced risks of thrombosis.
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PMID:Syndromes of hypercoagulability and thrombosis: a review. 805 29

Potent active-site inhibitors of human tissue factor-Factor VIIa (TF.FVIIa) have been selected from Alzheimer's amyloid beta-protein precursor inhibitor (APPI) Kunitz domain libraries displayed on phage. Eight randomized positions on the extended primary binding loop (P5 through P4') and positions 34 and 39 were examined in three separate libraries. Libraries contained from 3.2 x 10(5) to 3.2 x 10(6) potential variants resulting from replacing up to 5 positions with all 20 amino acids. Following 4 rounds of selection against FVIIa associated with immobilized tissue factor (TF), 12 clones from each library were sequenced. Variants were purified by trypsin affinity chromatography and reverse-phase high performance liquid chromatography, and characterized for their ability to inhibit TF.FVIIa chromogenic activity. Measured apparent equilibrium dissociation constants (Ki*) ranged from about 10 to 500 nM. From sequence and activity data, an overall consensus sequence, TF7I-C, was constructed by site-directed mutagenesis. TF7I-C differed from APPI at 4 key residues, T11P, M17L, S19L, and G39Y, and inhibited TF.FVIIa with a Ki* = 1.9 +/- 0.4 nM, which represented an increase in binding affinity of more than 150-fold compared to APPI. At 40 microM, TF7I-C prolonged the clotting times 3.5-fold in a prothrombin time assay and > 10-fold at 7 microM in an activated partial thromboplastin time assay. Prolongation of the activated partial thromboplastin time correlates with potent inhibition of FXIa (Ki* = 0.8 nM) and plasma kallikrein (Ki* = 1.2 nM). TF7I-C also inhibited plasmin (Ki* = 40 nM) and FXa (Ki* = 55 nM), but not activated protein C, thrombin, or FXIIa (Ki* > 10 microM each).
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PMID:Kunitz domain inhibitors of tissue factor-factor VIIa. I. Potent inhibitors selected from libraries by phage display. 807 37

Exposure of cultured endothelial cells to bacterial endotoxin induces an enhancement of cell procoagulant activity (PCA) and a simultaneous reduction of thrombomodulin activity (TM). We evaluated the effect of endotoxin on the expression of both endothelial PCA and TM in vivo, in rabbits. Animals were given a single i.v. injection of endotoxin (E. coli 0111:B4 LPS, W, 10-200 micrograms/kg); the thoracic aorta was harvested after 2 or 4 hours and placed in an ad hoc device to expose the endothelial surface only. Endotoxin treatment resulted in a dose-dependent increase of endothelial PCA (p < 0.001, at 100 micrograms/kg or more), which was totally dependent on factor VII and thus identified as tissue factor. In contrast, endothelial TM activity, as measured by the rate of thrombin-induced protein C activation, was similar in control and endotoxemic rabbits, even when the animals were given two injections (50 micrograms/kg, 24 h apart), or a continuous infusion (40 micrograms/kg/h during 4 hours) of endotoxin. To explore the effect of endotoxin on TM activity at the microcirculation level, we measured the extent of protein C activation in vivo, induced by a continuous infusion of low doses of thrombin (1 NIH U/kg/min for 60 min). Again, endotoxin administration was not associated with significant changes in TM-dependent protein C activation, as assessed by the anticoagulant activity present in a barium citrate plasma eluate obtained at the end of thrombin infusion. Although reduction of TM during persistent endotoxemia cannot be definitively excluded, our data support a major role of endothelial PCA in LPS-induced coagulative changes.
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PMID:Enhanced endothelial tissue factor but normal thrombomodulin in endotoxin-treated rabbits. 813 7


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