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Biomedical subjects

M F Scully

Publications and source records attributed to M F Scully.

At least 91 records · Page 5Linked to original sources
PubMed1985

Mechanisms of inhibition of platelet coagulant activity.

The plasma proteinase inhibitors are relatively ineffective in the inhibition of the activity of the platelet prothrombinase complex, due to the low rates of inhibition, and possibly due to the indirect protection from the potentiating effect of the vascular endothelium. The plasma proteinase inhibitors are more effective at inhibiting thrombin, thereby preventing the feedback activation of platelets and factor V and subsequent prothrombinase complex development. This may constitute a mechanism for the control of the development of the prothrombinase complex on the platelet surface. The protein C-thrombomodulin mechanism for the destruction of factor Va activity probably constitutes a major inhibitory mechanism for the prothrombinase complex in vivo.

Animals↗
PubMed1984

Inhibition of prothrombinase complex by plasma proteinase inhibitors.

The rate of inactivation of human coagulation factor Xa by the plasma proteinase inhibitors antithrombin III and alpha 1-antitrypsin has been studied in the presence of the accessory components which constitute the prothrombinase complex. The rate of inactivation of factor Xa by antithrombin III was found to be decreased in the presence of phospholipid vesicles with high affinity for factor Xa. The second-order rate constant for the reaction fell from 6.21 X 10(4) to 3.40 X 10(4) M-1 min-1 in the presence of 20 microM phospholipid. Purified factor Va had no effect on the rate of inactivation of factor Xa in the absence of phospholipid. In the presence of phospholipid, factor Va increased the protective effect displayed by phospholipid, further reducing the rate constant to 2.20 X 10(4) M-1 min-1. The rate of inactivation of factor Xa by alpha 1-antitrypsin was unaffected under these conditions. Platelet-bound prothrombinase complex was formed by incubation of factor Xa with washed human platelets activated by a mixture of collagen and thrombin. The prothrombinase activity was inhibited by antithrombin III was a second-order rate constant of 0.85 X 10(4) M-1 min-1. This rate was obtained in both the presence and absence of exogenous factor Va. Platelet factor 3 vesicles, isolated from platelet aggregation supernatants, also formed prothrombinase complex in the presence of factor Va, and this was inhibited by antithrombin III at the same rate as the platelet-bound complex. There was no protection of the platelet-bound prothrombinase complex from inhibition by alpha 1-antitrypsin.

Animals↗
PubMed1984

Identification of heparin cofactor II as the principal plasma cofactor for the antithrombin activity of pentosan polysulphate (SP54).

In antithrombin III depleted plasma only a slight reduction was observed in thrombin inhibitory activity due to potentiation by dermatan sulphate or by pentosan polysulphate (SP54). On gel filtration of normal plasma the peak of pentosan polysulphate dependent activity eluted with a higher apparent molecular weight than that observed with low concentrations of heparin. During purification of heparin cofactor II (1) good coincidence was observed between yields of its activity and the pentosan polysulphate dependent inhibitory activity and cochromatography of the two activities was observed also. Maximal second order rate constant of 2.5 X 10(8) M-1 min-1 (with apparent Kd of 1.8 microM) was found for the potentiation of the thrombin/heparin cofactor II interaction by pentosan polysulphate. A polysaccharide of high charge density may therefore potentiate heparin cofactor II activity and this may be of importance in vivo.

Antithrombins↗
PubMed1984

Effect of a pentosan polysulphate upon thrombin and factor Xa inactivation by antithrombin III.

The kinetics of inhibition of human and bovine alpha-thrombin and human factor Xa by antithrombin III were examined under pseudo-first-order conditions as a function of the concentration of pentosan polysulphate [a fully sulphated (beta 1-4)-linked D-xylopyranose with a single laterally positioned 4-O-methyl-alpha-D-glucuronic acid]. Double-reciprocal plots of the observed first-order rate constant against concentration of pentosan polysulphate gave straight lines, intercepts on the axes giving values for maximum increase in second-order rate constant (by calculation) and apparent dissociation constant. These values were: for human alpha-thrombin 1.52 X 10(7) M-1 . min-1 and 3.6 microM respectively, for bovine alpha-thrombin 6.56 X 10(6) M-1 . min-1 and 0.16 microM and for factor Xa 6.86 X 106 M-1 . min-1 and 20 microM. In the presence of pentosan polysulphate the dissociation constant for the initial complex of antithrombin III and thrombin was shown to be reduced from approx. 2 X 10(-3) M to 61 X 10(-6) M without apparent change in the limiting rate constant of 750 min-1. An oligosaccharide (primarily 8-10 saccharide units) prepared from heparin and with high affinity for antithrombin III but low potency in the thrombin-antithrombin III interaction did not diminish the rate of interaction catalysed by pentosan polysulphate. The catalysis was shown to be due to a weak electrostatic interaction, since it was completely reversed by concentrations of NaCl greater than 0.3 M. It is concluded that the mechanism is independent of the heparin high-affinity binding site on antithrombin III and is probably due to binding of the high-charge-density polysaccharide to the proteinase. It is calculated that the acceleration in rate achieved, although lower than that of heparin, approaches that required to be of physiological significance and may be of importance in the anticoagulation role of antithrombin III at sites of high charge density which may occur in vivo.

Animals↗
PubMed1984

Inhibition of the cerebroside sulphate (sulphatide)-induced contact activation reactions by platelet factor four.

Cerebroside sulphate or sulphatides, present in erythrocyte and leucocyte cell membranes, have recently been shown to be a potent activator of the contact phase of coagulation. Platelet factor-four (PF4), purified from human washed platelets, was found to inhibit the sulphatide induced APTT and plasma prekallikrein activation in a dose dependent manner. A four-fold increase in the sulphatide-APTT was observed in 156pM PF4 in the reaction mixture and 30% inhibition of prekallikrein activation was observed at 1.6nM. PF4 was found to be an approximately 1000-fold more potent inhibitor than protamine sulphate in inhibiting activation of clotting but was not as potent in inhibiting activation of prekallikrein. The physiological form of PF4 as released from platelets, was also found to cause inhibition of plasma prekallikrein activation, with 50% inhibition observed when the concentration of PF4 in plasma was 2.25 g/ml (0.29 M). The ability of PF4 to inhibit the contact activation reactions induced by sulphatides may be of some physiological significance in that when released during platelet activation and vessel wall injury, it may have a protective effect against the development of thrombosis.

Blood Coagulation↗
PubMed1984

The antiheparin effect of a heparinoid, pentosan polysulphate. Investigation of a mechanism.

A pentosan polysulphate [a fully sulphated (1-4)-beta-D-xylopyranose with a single laterally positioned 4-O-methyl-alpha-D-glucuronic acid] has been shown to inhibit the anticoagulant activity of high-affinity heparin as observed in plasma and when using purified enzyme and inhibitor. The activity was shown to be concentration-dependent with an apparent Ki of approx. 2 microM. The antiheparin property was not shown by a number of other anionic carbohydrates when tested. The rate of thrombin inhibition at 0.33 microM-heparin was reduced from 7.1 X 10(8) M-1 X min-1 in the absence of pentosan polysulphate to 2.3 X 10(8) M-1 X min-1 at 2 microM-pentosan polysulphate and to 0.3 X 10(8)M-1 X min-1 at 20 microM. Using the random bireactant model of heparin action [Griffiths (1982) J. Biol. Chem. 257, 13899-13902] it was observed that the pentosan polysulphate had no effect on the Km for antithrombin III (150 nM) but increased the Km for thrombin from 25 nM to 450 nM. A reduction in the inhibition rate by 17.3-fold predicted by substitution of these values into the general two-substrate reaction-rate equation was confirmed experimentally.

Antithrombin III↗
PubMed1984

The effect of collagen mediated platelet release on plasma prekallikrein activation.

Collagen mediated platelet aggregation caused -5.6 +/- 6.7% inhibition and +39.1 +/- 15.2% potentiation of prekallikrein activation in plasma from normal healthy volunteers between 20-40 and 50-65 years of age, respectively (n = 15, p less than 0.01). The amounts of platelets factor-four (PF4) released in the two groups were not significantly different. Collagen treatment in the presence of indomethacin caused +11.5 +/- 3.6% and +59.6 +/- 19.5% potentiation in the 20-40 and 50-65 age groups respectively (p less than 0.02). Adrenaline mediated platelet aggregation caused -55.2 +/- 7.1% and -35.2 +/- 8.3% inhibition in the 20-40 and 50-65 age groups, respectively. Collagen treatment of platelet-deficient-plasma and platelet-rich-plasma in EDTA also caused potentiation of prekallikrein activation. The results indicate that the observed degree of prekallikrein activation after platelet aggregation is a net result of the inhibitory effect of PF4 and the potentiatory effect of activated platelets. The potentiatory effect was greater after collagen treatment as compared to adrenaline treatment, and in the 50-65 age group as compared to the 20-40 age group.

Adult↗
PubMed1983

A platelet derived inhibitor of plasma prekallikrein activation.

Platelet products released by ADP mediated platelet aggregation or by repeated freeze-thawing of platelet-rich-plasma caused inhibition of the dextran sulphate induced activation of prekallikrein, measured amidolytically, in subsequently prepared platelet-poor-plasma. Platelet products did not inhibit the amidolytic activity of contact activated-plasma. Addition of antiserum to platelet factor-4 (PF4) neutralized the inhibitory effect of platelet products towards prekallikrein activation. When platelet released products were fractionated by heparin affinity chromatography, 93% of the PF4 applied and 86% of the inhibitory activity of the starting material was recovered in the high-affinity fraction.

Adenosine Diphosphate↗
PubMed1983

Anticoagulant and antiheparin activities of a pentosan polysulphate.

Pentosan polysulphate (PPS, Hemoclar, MW 6,700) was observed to have a low affinity for ATIII-Sepharose eluting at 0.3M NaCl. Tested in vitro it had, as previously reported, a low potency as an anticoagulant, about 10 times less than heparin on a weight for weight basis. Only the KCCT was affected by low concentrations of PPS unlike heparin by which both thrombin time and KCCT were affected. Upon injection of PPS subcutaneously (50mg) the heparin activity measured by chromogenic anti factor Xa and by KCCT was in the ratio of 2:1. When injected intravenously (40mg) into 3 healthy volunteers a significant prolongation of a modified prothrombin time was observed in 2 subjects. When PPS was added to heparin containing plasma it was observed to completely inhibit heparin at low concentrations (2:1 on a weight to weight basis) when measured in the thrombin and prothrombin time but not in the KCCT. The antiheparin effect of PPS was also observed in a purified system in obviating the heparin potentiation of the rate of inhibition of thrombin by antithrombin III. Observations showed that at higher concentrations of PPS it acted by directly inhibiting thrombin without the intervention of antithrombin III but also to potentiate the rate of fibrin monomer polymerization.

Anticoagulants↗
PubMed1983

Platelet activation during steady state sickle cell disease.

Previous reports have given conflicting conclusions of the role platelets may play in initiating vaso-occlusive sickle cell crisis. Seven patients homozygous for sickle cell hemoglobin, and seven age, race and sex matched controls were each studied on at least two occasions in a six week period of normal health. The number of platelets circulating as aggregates, the plasma concentration of beta-thromboglobulin (beta-TG) and platelet factor 4 (PF-4) were significantly elevated compared with controls. These findings were confirmed with a second series of fourteen patients and nine controls. Patient's platelets in plasma adjusted for both platelet number and citrate concentration aggregated more in response to low concentrations (0.4 and 1 microM) but less to higher concentrations (4 and 20 microM) of ADP and needed significantly more prostacyclin (PGI2) to inhibit ADP induced aggregation than did platelets from control subjects. There was no significant difference in plasma concentration of fibrinopeptide A and thromboxane (Tx)B2, nor in the platelet generation of TxB2 and release of serotonin and beta TG induced by aggregating agents. Thus, the platelets of patients with sickle cell anemia in the steady state are readily activated and respond in vivo by increased formation of aggregates and release of beta TG and PF-4.

Adenosine Diphosphate↗
PubMed1982

Fibronectin in fulminant hepatic failure.

Thirteen out of 17 patients with fulminant hepatic failure had plasma fibronectin concentrations below the normal range (194--472 micrograms/ml), the mean concentration in all 17 patients being 117.9 +/- SE 19.4 micrograms/ml. There was a significant negative correlation between plasma fibronectin concentration and aspartate aminotransferase activity, suggesting that fibronectin is consumed during clearance of hepatocyte debris. The reduced availability of fibronectin may be an important factor in the impaired function of Kuppfer cells in patients with fulminant hepatic failure.

Acute Disease↗