A study has been made of a low molecular weight semi-synthetic heparin analogue, A73025, that may be clinically useful as an antithrombotic agent because of its reported high specificity for antithrombin III. The clearance from the circulation of both heparin and the analogue has been studied in man following intravenous injection. Heparin obeyed almost first order kinetics when assayed using a specific anti-Xa assay and first order kinetics when measured with KCCT. At high concentrations the heparin analogue was cleared with first order kinetics when assayed both with the anti-Xa assay and with KCCT. At low concentrations the analogue produced between one half and two-thirds of the anti-Xa activity of an equal dose of heparin, producing only a small prolongation of KCCT. With increasing dose, the more specific anti-Xa potentiating effect of A73025 decreased because of a flattening of its anti-Xa dose-response curve. These results suggest that the analogue might be useful as an antithrombotic agent when it is used as a prophylactic agent.
Background: Oral anticoagulation (OAC) reduces stroke risk in patients with atrial fibrillation (AF) however it is often underutilized and sometimes refused by patients. Two inter-linking studies aimed to explore patients’ and physicians’ experiences of AF and OAC. Methods: Study 1: Three AF patient sub-groups were interviewed (n=11); accepted, refused, or discontinued OAC. Study 2: Four physician sub-groups (n=16) were interviewed: consultant cardiologists, general physicians, general practitioners and cardiology registrars. Data was analysed using IPA. Results: Three main themes comprised patients’ experiences: the initial consultation, life after the consultation, and patients’ reflections. Two main themes emerged from physicians’ experiences: communicating information and challenges with OAC prescription for AF. Discussion: This programme of work has illustrated the benefit of taking an in depth phenomenological approach to understanding the lived experience of the physician- patient consultation. This work has strengthened the evidence base and demonstrated that there is a need to target patients' and physicians' ability to communicate with each other in a comprehensible way.
Heparin and heparin oligosaccharides prepared by nitrous acid depolymerization were fractionated by affinity chromatography on immobilized antithrombin and by gel chromatography. The anticoagulant activities of high affinity heparin of Mr greater than or equal to 7,800 could be readily neutralized by the plasma protein histidine-rich glycoprotein (see also Lijnen, H.R., Hoylaerts, M., and Collen, D. (1983) J. Biol. Chem. 258, 3803-3808), whereas oligosaccharides falling below 18 saccharide units (Mr 5,400) became increasingly resistant to neutralization. An octasaccharide with characteristic marked ability to accelerate the inactivation of Factor Xa by antithrombin retained greater than 50% of its activity even at a histidine-rich glycoprotein/oligosaccharide molar ratio of 500:1. Histidine-rich glycoprotein, like the platelet-derived heparin neutralizing protein platelet factor 4 (Lane, D.A., Denton, J., Flynn, A.M., Thunberg, L. and Lindahl, U. (1984) Biochem J. 218, 725-732), therefore requires interaction with saccharide sequences in addition to the antithrombin-binding pentasaccharide of heparin in order to efficiently express its antiheparin activity. Heparan sulfate isolated from pig intestinal mucosa (HS I, Mr approximately 20,000) and from human aorta (HS II, Mr approximately 40,000) exhibited anti-Factor Xa activities of 180 and 20 units/micromol [corrected], respectively. A fraction corresponding to about 5% of HS I bound with high affinity to immobilized antithrombin and contained all of the anticoagulant activity of the starting material. While these heparan sulfates were readily neutralized by platelet factor 4, they were relatively resistant to neutralization by histidine-rich glycoprotein, although complete neutralization could be attained in the presence of molar excess of this protein. These findings may be of importance in relation (a) to the functional role of endogenous anticoagulant polysaccharides at the vascular wall and (b) to clinical situations in which heparin or heparin-related compounds are administered as exogenous anticoagulants.
<i>Background and Purpose:</i> Thrombomodulin is an integral part of the protein C anticoagulation pathway, and polymorphisms of its gene have been implicated in thrombosis. The point mutation G<sup>127</sup>→A has recently been found to be associated with myocardial infarction. <i>Methods:</i> We investigated this mutation in 465 patients with acute stroke and 353 control subjects. Genomic DNA containing the region of interest was amplified by PCR, and differing genotypes were identified by RFLP. <i>Results:</i> The A allele frequency was not statistically significantly different in the two groups, being 0.5% in the stroke group and 0.7% in the control group. <i>Conclusions:</i> The point mutation G<sup>127</sup>→A is an uncommon finding and, in this population, is unlikely to be a major risk factor for cerebrovascular disease.
There is uncertainty as to which activities of unfractionated heparin (UFH) and low MW heparin are responsible for their anticoagulant and antithrombotic properties. We have sought to answer this question by examining plasma samples taken during a recently conducted dose‐finding study of the low MW heparin, CY222, in haemodialysis for chronic renal failure. In this study, in vivo anticoagulant effect was assessed by measurement of plasma FPA levels. UFH was administered as a dose of 5000 iu bolus + 1500 iu/h maintenance infusion, while the effects of three doses of CY222 were studied (10000, 15000 and 20000 Institute Choay anti‐factor Xa u bolus, all with 1500 Institute Choay anti‐factor Xa u/h maintenance infusion). Anti‐factor Xa levels were determined by chromogenic substrate assay. Anti‐thrombin levels were determined by chromogenic substrate assay and by quantitation of catalysed thrombin–inhibitor complexes (using autoradiography). Analysis of the results indicate that plasma fibrinopeptide A (FPA) levels correlate with anti‐factor Xa ( r = 0.45) and anti‐thrombin (substrate) ( r = ‐0.63) levels of UFH, but only with the anti‐factor Xa levels ( r = ‐0.41) of CY222. These results suggest that the anti‐factor Xa assay is currently the most suitable assay for monitoring low MW heparins such as CY222 in humans.
Tissue factor pathway inhibitor (TFPI), the main inhibitor of initiation of coagulation, exerts an important anticoagulant role through the factor Xa (FXa)-dependent inhibition of tissue factor/factor VIIa. Protein S is a TFPI cofactor, enhancing the efficiency of FXa inhibition. TFPI can also inhibit prothrombinase assembly by directly interacting with coagulation factor V (FV), which has been activated by FXa. Because full-length TFPI associates with FV in plasma, we hypothesized that FV may influence TFPI inhibitory function. Using pure component FXa inhibition assays, we found that although FV alone did not influence TFPI-mediated FXa inhibition, it further enhanced TFPI in the presence of protein S, resulting in an ∼8-fold reduction in Ki compared with TFPI alone. A FV variant (R709Q/R1018Q/R1545Q, FVΔIIa) that cannot be cleaved/activated by thrombin or FXa also enhanced TFPI-mediated inhibition of FXa ∼12-fold in the presence of protein S. In contrast, neither activated FV nor recombinant B-domain-deleted FV could enhance TFPI-mediated inhibition of FXa in the presence of protein S, suggesting a functional contribution of the B domain. Using TFPI and protein S variants, we show further that the enhancement of TFPI-mediated FXa inhibition by protein S and FV depends on a direct protein S/TFPI interaction and that the TFPI C-terminal tail is not essential for this enhancement. In FXa-catalyzed prothrombin activation assays, both FV and FVΔIIa (but not activated FV) enhanced TFPI function in the presence of protein S. These results demonstrate a new anticoagulant (cofactor) function of FV that targets the early phase of coagulation before prothrombinase assembly.
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