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T W Barrowcliffe

Publications and source records attributed to T W Barrowcliffe.

At least 109 records · Page 6Linked to original sources
PubMed1986

Factor VIII concentrates contain factor VIII procoagulant antigen bound to phospholipid.

Fractionation of a human antibody to factor VIII: Ag by immunoabsorption with factor VIII/phospholipid (PL) complex has produced two pools of labelled Fab' fragments which can be used in fluid-phase immunoradiometric assays (IRMAs). One pool binds only to the PL-binding sites on factor VIII:Ag (and thus measures only that factor VIII:Ag in a sample not bound to PL), while the second binds to other antigenic sites. Parallel assays of factor VIII-containing materials using these two pools provide estimates of the proportion of factor VIII: Ag bound to PL in those materials. Five batches each of nine brands of factor VIII concentrates from eight different manufacturers were tested for PL-bound factor VIII:Ag by this method: all contained substantial amounts, ranging from 28% to 54% of the total factor VIII:Ag present. In addition, varying amounts of the factor VIII:Ag present in both non-activated and activated prothrombin complex concentrates (PCCs) from four manufacturers were PL-bound.

Antigens↗
PubMed1986

Low molecular weight heparin: a better drug?

Preliminary clinical trials suggest that at least some low molecular weight (LMW) heparins are as effective as heparin in preventing post-operative deep vein thrombosis, and need only be injected once a day. However, a firm basis does not exist for assigning potency estimates to different LMW heparins. Caution is therefore necessary in determining appropriate dosages for various clinical indications. Until the problems of standardization and dosage are resolved, LMW heparins are unlikely to achieve their potential usefulness, or prove safer than standard heparin.

Factor X↗
PubMed1985

Standardization of low molecular weight heparins: a collaborative study.

A collaborative study was carried out, in which eight laboratories each assayed eight low molecular weight (LMW) heparins against the International Standard (IS) for heparin. APTT assays and three types of anti-Xa method were used. The results of this study showed that: LMW heparins cannot be validly assayed against the IS by APTT or anti-Xa methods. Potencies of LMW heparins vs. the IS differed considerably between the four types of assay method used and also between different laboratories using the same type of method. Adoption of a single LMW heparin standard would improve validity, improve inter-laboratory variation, and largely abolish the differences between the three types of anti-Xa method. However, since calibration of a LMW heparin standard against the IS would give potencies that differ widely by the different assay methods, a single assay method such as the anti-Xa amidolytic, plasma, would need to be chosen for this calibration.

Antithrombins↗
PubMed1985

The effects of post-heparin plasma lipases on anti-Xa clotting activity.

The effects of hepatic triglyceride lipase (HTGL) and lipoprotein lipase (LPL) on the anti-Xa clotting activity of plasma were studied. LPL had no effect, but HTGL enhanced anti-Xa activity. This enhancement was shown to be due to a time-dependent action of HTGL on lipoproteins. These results could explain the increases in anti-Xa clotting activity previously observed after injection of heparin analogues, SSHA and SP54, which are potent releasers of lipase enzymes.

Animals↗
PubMed1985

Inhibition of antithrombin III by lipid peroxides.

A study was made of the inhibition of antithrombin III (At III) activity by lipid peroxides prepared from autoxidation of unsaturated fatty acids. Lipid peroxides markedly reduced the thrombin neutralising activity of plasma and purified At III with or without albumin carrier. Heparin Sepharose chromatography and heparin cofactor assays suggested that the primary target of lipid peroxides on the At III molecule may be the heparin binding site. Results from electrophoretic studies suggested that interaction between lipid peroxides and At III increased the negative charge of the At III molecule; however, no aggregation of the At III molecule was observed. Lipid peroxidation is being increasingly recognised as a factor in the pathogenesis of several disease states, and it is possible that local inhibition of At III by lipid peroxides could contribute towards the development of a thrombotic event.

Antithrombin III↗
PubMed1984

A collaborative study designed to establish the 4th International Standard for Heparin.

An international collaborative study, in which 22 laboratories participated, was carried out to establish a replacement for the International Standard for Heparin. A total of 248 assays were analyzed, including APTT, thrombin inhibition and anti-Xa assays, as well as pharmacopoeial assays. Overall, there was less than 5% difference in the mean potency estimates of the candidate preparations, by all assay methods. The freeze-dried preparation 82/502 demonstrated the closest parallelism by bioassay to the existing standard and was established by WHO as the 4th International Standard for Heparin, with an assigned unitage of 1780 i.u. per ampoule.

Animals↗
PubMed1984

Anticoagulant properties in vitro of heparan sulphates.

The anticoagulant properties in vitro of eight heparan sulphate preparations were studied using clotting (APTT, anti-Xa) and amidolytic (anti-Xa, anti-thrombin) assays. Activities ranged from very low levels (less than 5 iu/mg) up to values similar to those of heparin. Activities measured by APTT assay showed the best correlation with the sulphate to carboxylate ratio of the heparan sulphates. Highest activities were obtained in the anti-Xa clotting assay, these being approximately two-fold greater than activities in the anti-Xa amidolytic assay. Five of the heparan sulphate preparations were readily neutralised by protamine sulphate, whereas the three heparans with the lowest sulphate to carboxylate ratio were much more resistant to neutralisation. After fractionating each heparan sulphate into At III-binding and non-binding material, it was found that the anti-coagulant properties were associated only with the former. It is concluded that these properties are dependent on the activation of At III.

Animals↗
PubMed1984

Triglyceride-rich lipoproteins are responsible for thrombin generation induced by lipid peroxides.

Previous studies have shown that lipid peroxides promote thrombin generation in platelet-poor plasma. In the present study, it has been shown that triglyceride-rich lipoproteins, especially chylomicra of dietary origin, are responsible for this procoagulant activity. The generation of thrombin by lipid peroxides is also enhanced by their inhibitory action on antithrombin III. These results suggest a possible new relationship between dietary fat, lipid peroxidation and thrombus formation.

Antithrombin III↗
PubMed1984

High and low affinity heparin compared with unfractionated heparin as antithrombotic drugs.

A preparation of heparin was separated by affinity chromatography into two fractions: one of high ( HAH ) and the other of low (LAH) affinity to antithrombin III. These two fractions were compared with unfractionated heparin ( UFH ) by in vitro assay and their ability to impair experimental stasis thrombosis was also examined. Although the in vitro activity of HAH was double that of UFH , HAH was less effective than UFH as an antithrombotic drug; LAH was virtually inactive, both in vitro and in vivo. A mixture of 30 micrograms/kg of HAH and 50 micrograms/kg of LAH was as effective in preventing thrombosis as 80 micrograms/kg of UFH , and was more effective than 40 micrograms/kg of HAH alone, demonstrating that LAH potentiates the action of HAH in vivo.

Animals↗
PubMed1984

Low-affinity heparin potentiates the action of high-affinity heparin oligosaccharides.

Previous studies have shown that high-affinity (HA) heparin oligosaccharides, with molecular weights of 3,000-5,000, were less effective than unfractionated heparin in preventing serum-induced venous thrombosis in rabbits, using a Wessler stasis model. In the present study, a larger high-affinity fragment (M.Wt. 6,000-6,500) was also found to be less effective than unfractionated heparin as an antithrombotic agent. However, addition of 80 micrograms/kg low affinity (LA) heparin to 80 micrograms/kg of this HA fragment significantly potentiated its antithrombotic activity, and the antithrombotic action of the mixture was equivalent to that of unfractionated heparin. Significant potentiation of antithrombotic activity was also observed on the addition of LA heparin to a HA decasaccharide (M.Wt. 3,000-3,500) with anticoagulant activity only against Factor Xa. The LA heparin content of low molecular weight heparin fractions appears to be an important determinant of their antithrombotic activity.

Affinity Labels↗
PubMed1984

Fractionation of human antibody to factor VIII:C: and IRMA for phospholipid binding sites on factor VIII C:Ag.

Labelled Fab' fragments, derived from the plasma of a severe haemophiliac with antibody directed against factor VIII clotting antigen (VIII C:Ag), were fractionated by immunoabsorption with, first, a complex of phospholipid (PL) vesicles and factor VIII and, second, with factor VIII alone. Two pools of labelled anti-VIII C:Ag were obtained and were used in immunoradiometric assays (IRMAs) for VIII C:Ag. With one pool (non-PL-site antibody) VIII C:Ag assays were unaffected by pre-incubation of factor VIII with PL vesicles; however, binding of the second pool of antibody to VIII C:Ag was prevented by PL preincubation, indicating that these antibody molecules bind at or near a phospholipid binding site on VIII C:Ag (PL-site antibody). Assays of VIII C:Ag in an intermediate purity factor VIII concentrate with these two antibody pools indicate that more than one third of the VIII C:Ag may be bound to PL.

Antibodies↗
PubMed1983

Standardization of Factor VIII-III. Establishment of a stable reference plasma for Factor VIII-related activities.

An international collaborative study has been carried out to establish a reference plasma for Factor VIII-related activities. The freeze-dried reference plasma, coded 80/511, was assayed against fresh normal plasma, local standards and another freeze-dried plasma. There was good agreement between laboratories for the comparison of the two freeze-dried plasmas, but wide variation in the comparison of plasma 80/511 with fresh normal plasma and local standards, indicating the differences in Factor VIII content of local pooled plasmas. There were no significant differences between the one-stage and two-stage assays of VIII:C, or between electroimmunoassay (EIA) and immuno-radiometric (IRMA) assays of VIII:Ag. However, in VIII R:RCoF (ristocetin co-factor) assays, the aggregometry methods gave lower values than the macroscopic and counting methods for the comparison of freeze-dried against fresh normal plasmas. From the combined results of assays against each laboratory's fresh normal plasma, potencies were assigned to plasma 80/511 as follows: VIII:C 0.73 VIIIR:Ag 0.87 International Units VIIIR:RCoF 0.80 per ampoule VIIIC:Ag 0.95. Results from accelerated degradation studies indicated that losses of each VIII-related activity in plasma 80/511, when stored at -20 degrees C, should be less than 0.01% per year, indicating its suitability to serve as a long-term reference preparation. Plasma 80/511 has been established by the WHO Expert Committee on Biological Standardization as the 1st International Reference Preparation for Factor VIII-Related Activities in Plasma.

Antigens↗