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PubMed1984

Prorenin-renin conversion by the contact activation system in human plasma: role of plasma protease inhibitors.

Acid-pretreated normal human plasma generates renin activity at 0 degree C and neutral pH by the activation of prorenin. The activation is caused by kallikrein generated from prekallikrein by activated factor XII. Nonacidified plasma also generates renin at 0 degree C, but at a lower rate (cold-promoted activation). In normal plasma, 14% +/- 1% of prorenin (mean +/- SEM, n = 30) was activated during incubation at 0 degree C for 7 days (range 6% to 26%). Cold-promoted activation of prorenin was within the normal range in plasma deficient in factor XI, X, IX, VIIIC, VII, V, prothrombin, or high mol wt kininogen. Cold-promoted activation of prorenin was less than or equal to 1% in plasma deficient in factor XII or prekallikrein. Reconstitution of these plasmas with highly purified factor XII or prekallikrein restored normal prorenin activation. Correction of high mol wt kininogen deficiency had no effect. Thus cold-promoted activation of prorenin depends on the presence of factor XII and prekallikrein, whereas the other clotting factors are not essential. The influence of the inhibitors C1 esterase-inhibitor, alpha 2-macroglobulin, antithrombin III, and alpha 1-antitrypsin on the activation of prorenin was studied in factor XII-deficient plasma from which one or more of these inhibitors had been selectively removed by immunoadsorption. Factor XII was subsequently added, and the generation of renin at 37 degrees C was observed after complete factor XII-high mol wt kininogen-mediated activation of prekallikrein induced by dextran sulfate. No activation of prorenin was observed at 37 degrees C after depletion of C1 esterase inhibitor, alpha 2-macroglobulin, antithrombin III, or alpha 1-antitrypsin. When prekallikrein was activated in plasma depleted of both C1 esterase-inhibitor and alpha 2-macroglobulin, 6% of prorenin was activated in 2 hours at 37 degrees C. After additional depletion of antithrombin III, the activation increased to 47%. These results indicate that the contact activation system is capable of activating prorenin in plasma at physiologic pH and temperature when the three most important kallikrein inhibitors, C1 esterase-inhibitor, alpha 2-macroglobulin, and antithrombin III, are absent.

Binding Sites↗
PubMed1997

In vivo coagulation activation following infusion of highly purified factor XI concentrate.

The use of factor XI concentrates has been associated with thrombosis. Plasma markers of coagulation activation were measured before and 30, 60, 120 and 240 min after six infusions of the BPL factor XI concentrate. Five studies were completed before surgical intervention, one was undertaken in a patient with an intracerebral haemorrhage. Significant elevation of levels of fibrinopeptide A (FpA) (P < 0.05) and thrombin-antithrombin (TAT) were demonstrated following six infusions and prothrombin fragment F1.2 following four. Levels of all three markers had risen 60 min following concentrate administration and FpA levels remained elevated throughout the study period. Levels of D-dimer rose in four patients at 240 min. These results indicate significant thrombin generation by 60 min and subsequent plasmin generation consistent with coagulation activation by the factor XI concentrate. The greatest elevation of activation markers was seen in those subjects with pre-existing coagulation activation. We advise caution in the use of these products and awareness of the risks in patients who may already have activated coagulation states.

Adult↗
PubMed2006

Pregnancy and oral contraceptives in congenital bleeding disorders of the vitamin K-dependent coagulation factors.

Pregnancies and deliveries represent important hemostatic challenges for congenital coagulation disorders. The same is true for the assumption of oral contraceptives. Available information mainly deals with von Willebrand's disease, factor XI (FXI) deficiency and carriers of hemophilia A. Data concerning patients with congenital prothrombin complex factor deficiencies are very scanty. In the present study, data of a total of 27 women are presented, 11 patients with homozygous or double heterozygous deficiencies of FII, FVII and FX, together with 16 cases of hemophilia B carriers. The patients with FII, FVII or FX defects had a total of 14 pregnancies and often needed transfusion therapy. Proper management resulted in a decrease in postpartum bleeding and satisfactory fetal outcome. Elective cesarean delivery seems indicated only in recent years. Carriers of hemophilia B had a total of 19 pregnancies but showed no bleeding and needed no substitutive therapy. Searching the literature, we discovered only 9 additional patients with prothrombin deficiency or FX deficiency, having a total of 16 pregnancies. On the contrary, there were at least 17 additional patients with FVII deficiency, with a total of 21 pregnancies. The management of the diseases has been variable, but in substantial agreement with the personal observations. Oral contraceptive therapy was administered in some of our patients and in a few additional cases described in the literature. Medication was always well tolerated and patients who took it for a long period of time showed a decrease in menometrorrhagia and an improvement in hematocrit levels. This led to a decrease in transfusional needs and to improved general conditions.

Adult↗
PubMed1975

A new method for the assay of factor XI in plasma and the preparation and use of a new artificial substrate.

An improved method for the one-stage assay of factor XI in plasma has been proposed; it is reproducible and compares well with an old, established method.A short investigation into the preparation and use of artificially prepared factor XI-deficient plasma has been carried out: this substrate can be used as an alternative to the congenitally deficient substrate.

Analysis of Variance↗
PubMed1996

Coagulation abnormalities in patients with Gaucher's disease: effect of therapy.

Various coagulation defects have been associated with Gaucher's disease, including factor IX deficiency and acquired von Willebrand's disease (VWD). We performed repeated coagulation assays in 9 patients with Gaucher's disease over a period of 2 years. The prothrombin time (PT) and fibrinogen levels were normal in 8 of 9 patients, while the partial thromboplastin time (PTT) was abnormal in 5 of 9; all mixing PTT tests showed correction. Factor IX was normal repeatedly in the 7 of 7 patients tested. In contrast, factor XI was decreased in 3 of 9 patients assayed. Anticardiolipin (ACL) IgM was normal in all patients. ACL IgG was highly variable; levels were abnormal at least once in 6 of 8 patients, but were also normal at least once in 7 of 8 patients. Factor VIII was also quite variable: levels were decreased at least once in 4 of 9 patients, and normal at least once in 8 of 9 patients. Von Willebrand factor antigen (VWF Ag) studies were normal in 7 of 8 patients, but VWF activity was decreased at least once in 4 of 8 patients. In some patients, these problems could be overcome by specimen dilution. In ony 1 patient was VWF Ag decreased; this patient had a factor VIIIC level of 13% , and VWF activity of 18.7%. Coagulation assays performed before and after alglucerase administration failed to demonstrate any significant improvement in these assays, and neither was there a consistent improvement over the duration of therapy. We suggest that previously reported decreases in factor IX and VWF may be secondary to the interfering presence of increased cerebroside levels. Caution must be used in the interpretation of clotting assays in the patient with Gaucher's disease.

Antibodies, Anticardiolipin↗
PubMed2001

RETRACTED: Factor XI binding to the platelet glycoprotein Ib-IX-V complex promotes factor XI activation by thrombin.

Factor XI binds to high affinity sites on the surface of stimulated platelets where it is efficiently activated by thrombin. Here, we provide evidence that the factor XI binding site on platelets is in the glycoprotein (GP) Ibalpha subunit of the GP Ib-IX-V complex as follows. 1) Bernard-Soulier platelets, lacking the complex, are deficient in factor XI binding; 2) two GP Ibalpha ligands, SZ-2 (a monoclonal antibody) and bovine von Willebrand factor, inhibit factor XI binding to platelets; 3) by surface plasmon resonance, factor XI bound specifically to glycocalicin (the extracellular domain of GP Ibalpha) in Zn(2+)-dependent fashion (K(d)( app) approximately 52 nm). We then investigated whether glycocalicin could promote factor XI activation by thrombin, another GP Ibalpha ligand. In the presence of high molecular weight kininogen (45 nm), Zn(2+) and Ca(2+) ions, thrombin activated factor XI in the presence of glycocalicin at rates comparable with those seen in the presence of dextran sulfate (1 microg/ml). With higher high molecular weight kininogen concentrations (360 nm), the rate of thrombin-catalyzed factor XI activation in the presence of glycocalicin was comparable with that on activated platelets. Thus, factor XI binds to the GP Ib-IX-V complex, promoting its activation by thrombin.

Animals↗
PubMed1983

Isolation and functional characterization of the active light chain of activated human blood coagulation factor XI.

Human blood coagulation Factor XIa was reduced and alkylated under mild conditions. The mixture containing alkylated heavy and light chains was subjected to affinity chromatography on high Mr kininogen-Sepharose. Alkylation experiments using [14C]iodoacetamide showed that a single disulfide bridge between the light and heavy chains was broken to release the light chain. The alkylated light chain (Mr = 35,000) did not bind to high Mr kininogen-Sepharose while the heavy chain (Mr = 48,000), like Factors XI and XIa, bound with high affinity. The isolated light chain retained the specific amidolytic activity of native Factor XIa against the oligopeptide substrate, pyroGlu-Pro-Arg-p-nitroanilide. Km and kcat values for this substrate were 0.56 mM and 350 s-1 for both Factor XIa and its light chain, and the amidolytic assay was not affected by CaCl2. However, in clotting assays using Factor XI-deficient plasma in the presence of kaolin, the light chain was only 1% as active as native Factor XIa. Human coagulation Factor IX was purified and labeled with sodium [3H]borohydride on its carbohydrate moieties. When this radiolabeled Factor IX was mixed with Factor XIa, an excellent correlation was observed between the appearance of Factor IXa clotting activity and tritiated activation peptide that was soluble in cold trichloroacetic acid. Factor XIa in the presence of 5 mM CaCl2 activated 3H-Factor IX 600 times faster than Factor XIa in the presence of EDTA. In the absence of calcium, Factor XIa and its light chain were equally active in activating 3H-Factor IX. In contrast to Factor XIa, the light chain in this reaction was inhibited by calcium ions such that, in the presence of 5 mM CaCl2, Factor XIa was 2000 times more effective than its light chain. Neither phospholipid nor high Mr kininogen and kaolin affected the activity of Factor XIa or its light chain in the activation of 3H-Factor IX. These observations show that the light chain region of Factor XIa contains the entire enzymatic active site. The heavy chain region contains the high affinity binding site for high Mr kininogen. Furthermore the heavy chain region of Factor XIa plays a major role in the calcium-dependent mechanisms that contribute to the activation of Factor IX.

Acetamides↗
PubMed1996

In vivo demonstration in humans that large postprandial triglyceride-rich lipoproteins activate coagulation factor VII through the intrinsic coagulation pathway.

In vitro studies in purified plasma systems have suggested that triglyceride-rich lipoproteins such as chylomicrons, very low density lipoproteins, and their remnants promote activation of factor VII through activated factor XII (XIIa) and the intrinsic coagulation pathway. We specifically examined the roles of factors XII, XI, and IX in activation of factor VII during alimentary lipemia in vivo in humans and addressed the issue of whether generation of activated factor VII (VIIa) is accompanied by increased thrombin production. For this purpose XIIa, factor IX activation peptide (IXP), VIIa, prothrombin fragment 1 + 2 (F1 + 2), and thrombin-antithrombin complex (TAT) were determined in plasma samples taken before and 3, 6, and 9 hours after intake of a mixed meal type of oral fat load in 24 healthy men The VIIa response to fat intake was also determined in 7 patients with single coagulation-factor deficiency, of whom 2 were deficient in factor XII, 2 in factor XI, and 3 in factor IX. Postprandial activation of factors IX and VII occurred in the healthy individuals, whereas the plasma levels of XIIa did not change in response to the test meal. Of note, plasma concentrations of F1 + 2 were unaltered during alimentary lipemia, and TAT levels showed a small decrease (P < .05) in the 3-hour sample compared with the fasting level, indicating that thrombin generation is not stimulated in the postprandial state, despite the generation of activated factor IX (IXa) and VIIa. Factor VIIa increased in the postprandial period in the 2 factor XII-deficient patients who underwent the oral fat tolerance test but appeared to remain unchanged in the factor XI- and factor IX-deficient patients. Therefore, the current concept that activation of factor XII plays a pivotal role in initiating the sequence of events linking postprandial lipemia to activation of factor VII is contradicted by the present study. Whether activation of factor XI by triglyceride rich lipoproteins initiates these reactions needs to be demonstrated in future studies.

Adult↗
PubMed1999

Systemic causes of excessive uterine bleeding.

In assessing a patient with excessive uterine bleeding, the clinician should consider systemic causes in the differential diagnosis. Both hereditary and acquired conditions can result in mucous membrane bleeding, including menorrhagia, epistaxis, and gum bleeding, as well as excessive bruising. Among hereditary conditions, von Willebrand disease (vWD) is by far the most common, affecting an estimated 1% of the population worldwide. It is important to consider the possibility of vWD, and to establish the proper diagnosis (including subtype), as safe, effective, and easy-to-use treatment is available for most persons with this disorder. This review also covers a number of other systemic conditions that can be manifested by excessive uterine bleeding, including congenital deficiency of factor XI, idiopathic thrombocytopenic purpura and other acquired platelet disorders, acquired autoantibodies against factor VIII (FVIII), and vitamin K deficiency states.

Female↗
PubMed2001

Gene targeting in hemostasis. factor XI.

Factor XI (FXI) is the zymogen of a plasma serine protease (FXIa) that contributes to hemostasis by activating factor IX (FIX). This reaction appears to be important for sustaining thrombin production after initial fibrin formation, to consolidate and protect fibrin clots from degradation by fibrinolysis. Humans with congenital FXI deficiency have a variable propensity to bleed after trauma or surgery, but do not experience the "spontaneous" hemorrhage in joints and soft tissue characteristic of hemophilia (FVIII or FIX deficiency). Mice homozygous for a disruption of the FXI gene (FXI-/-) have prolonged activated partial thromboplastin times and no detectable plasma FXI activity. Like their human counterparts, FXI-/- animals are generally healthy, reproduce normally, and do not develop spontaneous hemorrhage. In tail bleeding time assays, FXI-/- animals may have slightly prolonged bleeding compared to FXI+/+ and FXI+/- animals, however, a consistent hemostatic deficit has not been identified. More impressive results are obtained when FXI-/- mice are crossed with protein C deficient mice. Severe FXI deficiency partially ameliorates the devastating hypercoagulable state associated with severe protein C deficiency, indicating that FXI plays a role in certain thrombotic conditions.

Animals↗