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T W Barrowcliffe

Publications and source records attributed to T W Barrowcliffe.

At least 91 records · Page 5Linked to original sources
PubMed1989

Relative efficacy of heparin and related glycosaminoglycans as antithrombotic drugs.

In a standardized animal model, unfractionated heparin (UFH) prevents venous thrombogenesis at a dose of 80 micrograms/kg. Oligosaccharide fragments of heparin, with very high anti-Xa activity both in vitro and in ex vivo plasma samples were less effective than UFH in preventing thrombosis. A decasaccharide fragment was virtually inactive in impairing thrombosis at this dose, although a 20-22 monosaccharide fragment showed some impairment. Dermatan sulfate, which has no anti-factor Xa activity, partially impairs both thrombin generation and stasis thrombosis. However, dermatan sulfate could not suppress thrombin generation below about 35% of control at the doses studied. Neither oligosaccharides nor dermatan sulfate were as effective on a weight basis as UFH in impairing thrombosis, particularly after 20 minutes' stasus. Maximal antithrombotic effects are achieved when both factor Xa and thrombin are inhibited. Drugs which act primarily on factor Xa (oligosaccharides) or thrombin by non-ATIII pathways (dermatan sulfate) are less efficient than UFH as antithrombotic drugs.

Animals↗
PubMed1989

Assay discrepancies with highly purified factor VIII concentrates.

We have assayed two different monoclonal-antibody-purified concentrates (A and B) and one conventional concentrate (C), against the 3rd International Standard for factor VIII concentrate, using one-stage, two-stage and chromogenic methods. One-stage assays performed with immunodepleted plasmas gave lower potencies than with haemophilic plasma for all concentrates, though the discrepancies were most marked for the two highly purified products. The absence of von Willebrand factor in one of the immunodepleted plasmas appeared to contribute towards the low potencies observed. In addition, potencies of product A were 50% higher by one-stage assays (haemophilic plasma) than by two-stage or chromogenic methods. These results indicate the need for careful evaluation of assay methodologies for assessment of factor VIII:C activity in highly purified concentrates.

Blood Proteins↗
PubMed1988

Heparin and bleeding: an association with lipase release.

The effects of four sulphated polysaccharides on bleeding time and lipase release in rabbits have been compared. Unfractionated heparin (UFH) and pentosan polysulphate both gave significant prolongation of bleeding times and high lipase release. Low molecular weight heparin had reduced effects on bleeding time and lipase release, while dermatan sulphate had no influence on either parameter. There was a highly significant correlation (r = 0.97) between these two measurements. These results suggest that the same structural features influence both the haemorrhagic and lipase-releasing properties of sulphated polysaccharides.

Animals↗
PubMed1988

Factor VIII procoagulant protein interacts with phospholipid vesicles via its 80 kDa light chain.

In a previous report, we detailed fractionation of polyclonal human anti-Factor VIII:C into a component directed exclusively against the phospholipid-binding site on Factor VIII (PL-site antibody) and another directed at other sites (non-PL-site antibody). The location on the F.VIII molecule of its PL-binding site has now been studied by two different methods using this fractionated 125I-labelled anti-F.VIII:C Fab'. The first method was modified from that of Weinstein et al. (Proc Natl Acad Sci USA 1981; 78: 5137-41), involving electrophoresis of F.VIII peptide-125I-Fab' A/F.VIII immunocomplexes in SDS-polyacrylamide gels. PL-site antibody reacted with F.VIII peptides of apparent Mr approximately 80 kDa and sometimes 160 kDa in plasma and concentrate, but not with larger peptides. Non-PL-site antibody, however, reacted with a range of peptides of apparent Mr 90 kDa to 280 kDa. In addition, when purified F.VIII containing heavy and light chains (HC + LC), and isolated LC peptides were analysed, PL-site antibody bound to LC peptides whereas non-PL-site antibody did not. The second method used the antibody pools in immunoradiometric assays (IRMA's) of purified F.VIII peptides. Both labels measured similar amounts of F.VIII:Ag in a sample of purified F.VIII containing both HC and LC; on assaying an HC preparation, however, PL-site label measured only 2% of F.VIII:Ag found by non-PL-site label, indicating that PL-binding sites are absent in HC preparations. These results indicate that F.VIII binds to PL via its 80 kDa light chain.

Antigen-Antibody Complex↗
PubMed1988

An international standard for low molecular weight heparin.

An international collaborative study has been carried out with the aim of establishing an international standard for low molecular weight (LMW) heparin. Three preparations of LMW heparin were assayed against the International Standard for unfractionated heparin (UFH) by 25 laboratories in 13 countries, using nine different assay methods. The results confirmed previous findings of non-parallel assays, wide interlaboratory variability and differences between methods when LMW heparins are assayed against a UFH standard. Use of one of the LMW heparins as a standard for the other two gave parallel assays and much closer agreement between laboratories. The preparation in ampoules coded 85/600 was selected as likely to give the best agreement with the largest number of LMW heparins; potencies were assigned by taking the mean of all the anti-Xa assays, and the mean of the thrombin and APTT assays, to represent the two major groups of activities. Preparation 85/600 has been established by WHO as the 1st International Standard for LMW heparin, with potencies of 1,680 iu/ampoule by anti-Xa assays and 665 iu/ampoule by thrombin inhibition and APTT assays.

Antithrombin III↗
PubMed1988

Low molecular weight heparins: antithrombotic and haemorrhagic effects and standardization.

Measurement of the in vitro anticoagulant activities of low molecular weight (LMW) heparins against an unfractionated heparin (UFH) standard has given problems of non-parallel assays, wide variability between laboratories and differences between methods. These problems have been largely overcome by establishment of a new LMW heparin standard against which other LMW heparin can be compared. The LMW heparin standard is calibrated with two separate potencies, one for anti-Xa and the other for thrombin inhibition assays. Animal studies have shown a correlation between the anti Xa and antithrombotic activities of several LMW heparins but, below a M.Wt. of approximately 4,000, this correlation breaks down. This may be partly due to the method of measurement of anti-Xa activity and partly due to the inability of very LMW fragments to potentiate thrombin inhibition, which has recently been shown to be an important component of antithrombotic action. However, substances with either anti-Xa activity alone or thrombin inhibitory capacity alone are less effective antithrombotic agents than heparin. Several studies in animals have shown that LMW heparins give less enhancement of bleeding than UFH, but this does not seem to be due to their anticoagulant effects and may be related to their relative effects on platelets.

Animals↗
PubMed1987

The development and characterisation of antibodies to human factor VIII in haemophilic dogs.

Four haemophilic dogs received infusions of human factor VIII concentrates, and developed inhibitors to human F VIII. These inhibitors cross-reacted with canine F VIII with parallel increases and decreases in titre. Cross-reaction was also found to porcine F VIII but changes in titre did not correlate with anti-human and anti-canine titres. These inhibitors were found to be immunoglobulins, and antibodies were detected against other proteins found in concentrates. Kinetic studies showed that in all four dogs the F VIII inhibitors were Type II antibodies. One of the dogs behaved as a "high-responder", whilst another was more analogous to a "low-responder" patient. Phospholipid protection experiments in vitro demonstrated that some antibodies could be prevented from inhibiting F VIII, and porcine F VIII was particularly well protected against inhibition.

Animals↗
PubMed1987

The effect of Ca2+, phospholipid and factor V on the anti-(factor Xa) activity of heparin and its high-affinity oligosaccharides.

The influence of Ca2+, phospholipid and Factor V was determined on the rate of inactivation of Factor Xa by antithrombin III, in the absence and in the presence of unfractionated heparin and of three high-affinity heparin oligosaccharides in the Mr range 1500-6000. In the absence of heparin the addition of Ca2+, phospholipid and Factor V caused a 4-fold decrease in rate of inactivation of Factor Xa. As concentrations of unfractionated heparin were increased the protective effect of Ca2+/phospholipid/Factor V was gradually abolished, and at a concentration of 2.4 nM there were no differences in rates of neutralization of Factor Xa in the presence or absence of Ca2+, phospholipid and Factor V. In contrast, heparin decasaccharide (Mr 3000) and pentasaccharide (Mr 1500) fragments were unable to overcome the protective effect of Ca2+/phospholipid/Factor V; in the presence of these components their catalytic efficiencies were 16-fold and 40-fold less respectively than that of unfractionated heparin. A heparin 20-22-saccharide fragment (Mr approx. 6000) gave similar inactivation rates in the presence and in the absence of Ca2+/phospholipid/Factor V. Human and bovine Factor Xa gave similar results. These results indicate that in the presence of Ca2+/phospholipid/Factor V optimum inhibition of Factor Xa requires a saccharide sequence of heparin additional to that involved in binding to antithrombin III. The use of free enzyme for the assessment of anti-(Factor Xa) activity of low-Mr heparin fractions could give misleading results.

Antithrombin III↗
PubMed1987

Procoagulant activity of platelet arachidonic acid metabolites.

1 Arachidonate metabolites have been extracted from indomethacin-treated human platelets after incubation with arachidonic acid. 2 After separation from platelet phospholipids, the extracts promoted the generation of large amounts of thrombin in normal plasma, but not in plasma devoid of lipoproteins. 3 The procoagulant activity was associated with a minor component of the mixture, which was active at concentrations below 10 micrograms ml-1. 4 The activity was similar to that of autoxidised arachidonic acid previously described. 5 Platelet arachidonic acid metabolites could play a role in the coagulation system.

Arachidonic Acids↗
PubMed1987

Anti-Xa activity of human hepatic triglyceride lipase.

Human hepatic triglyceride lipase (HTGL), purified from plasma obtained after heparin injection, markedly enhanced the anti-Xa clotting activity of normal plasma. This was shown to be caused by direct inhibition of factor Xa clotting activity by HTGL, although the amidolytic activity of factor Xa was unaffected. Preincubation of factor Xa with CaCl2 and phospholipid reduced the rate of inhibition of HTGL, indicating that phospholipid-binding sites may be involved. Heparin, and low-affinity heparin, reduced the anti-Xa activity of HTGL, suggesting that heparin and factor Xa compete for the same binding sites on the lipase molecule. These results suggest that at least part of the enhanced anti-Xa clotting activity observed after injection of heparin and heparin analogues is caused by the release of HTGL. This release could contribute toward the anticoagulant and antithrombotic actions of these drugs.

Animals↗
PubMed1986

Anticoagulant activities of pentosan polysulphate (Hémoclar) due to release of hepatic triglyceride lipase (HTGL).

Subcutaneous injections of 50 mg pentosan polysulphate (Hémoclar) were given to normal volunteers and the effects on anti-Factor Xa activity, thrombin generation and lipase release measured. Concentrations of pentosan polysulphate were measured by a competitive binding assay and the mean peak level found to be 1.6 micrograms/ml. Anti-Xa clotting activity rose to 0.034 iu/ml and thrombin generation induced by lipid peroxides was inhibited by approximately 50%. Neither of these effects could be accounted for by the direct action of pentosan polysulphate at the concentrations measured. Pentosan polysulphate was very effective in releasing lipase, approximately 70-80% of the total enzyme activity being due to hepatic triglyceride lipase (HTGL). In vitro addition of purified HTGL to plasma markedly enhanced anti-Xa clotting activity, and caused a 70% inhibition of lipid peroxide induced thrombin generation. Anti-Xa activity of post-injection plasma was increased rather than neutralised by addition of polybrene, and this effect could be mimicked by addition of polybrene to plasma containing pentosan polysulphate and purified HTGL. It is concluded that, when given in low doses subcutaneously, pentosan polysulphate acts as an indirect anticoagulant, its major effects being due to release of HTGL.

Adult↗