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Biomedical subjects

C R Hay

Publications and source records attributed to C R Hay.

At least 37 records · Page 2Linked to original sources
PubMed1997

The treatment of bleeding in acquired haemophilia with recombinant factor VIIa: a multicentre study.

Recombinant factor VIIa was used to treat 38 patients with acquired haemophilia participating in the Novoseven compassionate-use program. 19 were male, median age 59, range 2-89 years. The median pre-treatment anti-human (H) and anti-porcine (P) inhibitor titre was H 43 BU/ml (range 1-4500) and P 4.5 BU/ml (range 0-1600). Recombinant factor VIIIa was used as first-line therapy for 14 bleeding episodes and as salvage-therapy for 60 episodes which failed to respond to blood-product therapy given for a median of four days (range 1-21 days) prior to treatment with rVIIa. Pre-rVIIa treatment was not reported for four episodes. The indications for treatment were 7 haemarthroses, 40 muscle haematomas, 20 urinary or GI haemorrhages and 3 surgical interventions. The median starting dose of rVIIa was 90.4 microg/kg (range 45-181). A median of 28 doses (range 1-541) were given per episode, over a median 3.9 days (range 0-43). Efficacy was assessed clinically 8 and 24 h after the start of rVIIa and at the end of treatment. A good response was obtained in all 14 bleeds for which rVIIIa was used as first-line therapy. The response after 24 h of rVIIa salvage-therapy for 60 bleeds was good in 75%, partial in 17% and poor in 8%. Efficacy was unreported in 4 cases. The median prothrombin time (PTT) shortened from 12 s (range 9.3-20) pre-treatment to 8.8 s (range 6-14) during treatment. The clinical response did not correlate with the dose of rVIIa used, the type of bleed or the degree of shortening of the PTT following rVIIa infusion. Three patients died from haemorrhagic complications of acquired haemophilia. This mortality of 7.9% is lower than previously reported for this condition. Although one patient developed DIC during treatment with rVIIa, this was probably attributable to hypovolaemic shock, massive transfusion and the use of PCCs. This study demonstrates that rVIIa is a safe, useful and effective treatment for bleeding in patients with acquired haemophilia.

Adolescent↗
PubMed1996

Inhibition of collagen-induced platelet aggregation as the result of cleavage of alpha 2 beta 1-integrin by the snake venom metalloproteinase jararhagin.

Jararhagin is a high-molecular-mass (52 kDa) haemorrhagic metalloproteinase from Bothrops jararaca venom and a member of the metalloproteinase/disintegrin/cysteine-rich protein family. The disintegrin domain of jararhagin has been implicated in the inhibition of platelet responses to collagen by a mechanism that is not entirely known. The present investigation demonstrates that both active and 1,10-phenanthroline-inactivated jararhagin inhibit platelet aggregation by collagen with an IC50 of 40 and 140 nM respectively. The apparently higher inhibitory effect of the active enzyme clearly indicates that, in addition to the disintegrin region, the metalloproteinase domain of jararhagin also participates in this inhibition. As collagen interacts with platelets via alpha 2 beta 1-integrin, we investigated the effects of jararhagin on this integrin using selected function-blocking monoclonal antibodies against both of its subunits. Flow cytometry of platelets treated with native jararhagin and immunoprecipitation of platelet surface glycoproteins from lysates after jararhagin treatment showed an apparently selective reduction of alpha 2 beta 1-integrin immunoreactivity with both anti-alpha 2 and anti-beta 1 monoclonal antibodies. The loss of immunoreactivity was not due to integrin internalization, since it also took place in cytochalasin D-treated platelets. Here we show that jararhagin cleaved isolated alpha 2 beta 1-integrin resulting in the generation of a 115 kDa beta 1 fragment. We therefore propose that the inhibition by jararhagin of platelet response to collagen is mediated through the binding of jararhagin to platelet alpha 2-subunit via the disintegrin domain, followed by proteolysis of the beta 1-subunit with loss of the integrin structure (conformation) necessary for the binding of macromolecular ligands.

Cell Membrane↗
PubMed1996

Insights into the mechanism of haemorrhage caused by snake venom metalloproteinases.

Local and systemic haemorrhage are common consequences of crotaline and viperine envenoming. Several studies carried out using purified toxins have indicated that local haemorrhage can be attributed to a distinct class of venom metalloproteinases. Analyses of their cDNAs predict multi-domain enzymes, with an N-terminal metalloproteinase domain, a disintegrin-like domain and a Cys-rich C-terminus. Haemorrhagic metalloproteinases are responsible for degrading proteins of the extracellular matrix and they also have cytotoxic effects on endothelial cells. However, to date very few investigations have been carried out on the effects of venom haemorrhagic metalloproteinases on components of the haemostatic system. We describe here the effects of a high molecular weight haemorrhagic metalloproteinase, jararhagin, from the venom of a South American pit viper Bothrops jararaca, on platelet and plasma components involved in haemostasis. Jararhagin, which is not inhibited in plasma, causes the loss of the platelet collagen receptor alpha 2 beta 1 integrin (gpIa/IIa or VLA-2) and degrades the adhesive plasma protein von Willebrand factor. Alterations of these haemostatic components are known to result in bleeding. This suggests that venom haemorrhagic metalloproteinases, in addition to causing local bleeding, may also contribute to systemic haemorrhage.

Amino Acid Sequence↗
PubMed1996

Von Willebrand factor, thrombomodulin, thromboxane, beta-thromboglobulin and markers of fibrinolysis in primary Raynaud's phenomenon and systemic sclerosis.

OBJECTIVE: To determine whether measurement of different markers of endothelial damage, activation of coagulation, and platelet activation might differentiate between patients with primary Raynaud's phenomenon (PRP), limited cutaneous and diffuse systemic sclerosis (lcSSc and dSSc), and healthy control subjects. METHODS: Under carefully controlled conditions, fasting blood was drawn from 19 healthy control subjects, 10 patients with PRP, 17 with lcSSc and nine with dSSc for measurement of the following: von Willebrand factor (VWF) and soluble thrombomodulin as markers of endothelial damage/activation, thromboxane (as thromboxane B2) and beta-thromboglobulin as markers of platelet activation, and tissue plasminogen activator antigen, tissue plasminogen activator activity and plasminogen activator inhibitor-1 (PAI-1) as markers of fibrinolysis. RESULTS: VWF was increased significantly in patients with SSc, and there was also a linear trend for thromboxane and tissue plasminogen activator antigen (in addition to VWF) to differentiate between different subgroups of patients with Raynaud's phenomenon. Patients with dSSc had the highest values. A combined index of VWF and thromboxane showed a highly significant trend across the four groups studied. CONCLUSION: VWF, and to a lesser extent thromboxane and tissue plasminogen activator antigen, are associated with disease severity in patients with Raynaud's phenomenon. Prospective studies are now required to establish if these parameters can be used as markers of disease progression.

Adult↗
PubMed1996

Safety profile of porcine factor VIII and its use as hospital and home-therapy for patients with haemophilia-A and inhibitors: the results of an international survey.

A multicentre retrospective survey was conducted to re-assess the use of porcine factor VIII (HYATE:C), its side effects and the selection of patients for regular or home-therapy. 15,152,000 units of HYATE:C were used by 154 patients. The median inhibitor cross-reactivity to porcine VIIIC of 137 patients was 15%, 27% of patients lacking cross-reactivity. An absent, intermediate or brisk specific antiporcine anamnestic response was observed in 29, 40 and 31% of patients respectively. Seven patients were treated on-demand as home-therapy for a median 6.2, range 1.5-13 years, 23 further patients were treated regularly in hospital for a median of 3, range 2-7 years. This group used 8,319,000 U of porcine VIIIC for 2,000 bleeding episodes. The incidence of transfusion reactions was 0.001%, 0.64% and 2.3%, for domiciliary infusions, infusions in multiply treated in-patients, and unselected in-patient infusions, respectively. The risk of reactions was dose-related. A post-infusion fall in platelet count was common, but usually transient and clinically insignificant. This was also dose-related (r = -0.64, p = 0.002). Marked reductions in platelet count were occasionally seen, usually with intensive replacement therapy. The relative lack of side effects observed amongst patients treated at home is attributable to the low, median 33 U/kg, dose used by this group. A subgroup of inhibitor patients, identifiable by their absent or modest anamnestic response to porcine factor VIII may be treated regularly and safely with this product in small doses, over a period of years.

Animals↗
PubMed1996

Continuous infusion of factor VIII for surgery and major bleeding.

In a clinical trial, 24 patients with haemophilia A who needed surgery or had suffered severe bleeding were treated by continuous infusion of Monoclate P, a factor VIII concentrate that is immunopurified by monoclonal antibodies. Continuous infusion of Monoclate P began with a dose of 2 U/kg per h that was adjusted according to the results of factor VIII assays to achieve a factor VIII target level of 100 IU/dl for 2 days and then 80 IU/dl for 5 days. The safety, efficacy, and economics of this approach were assessed. No haemorrhagic episodes were observed. The continuous infusion was convenient and had the advantage of producing steady-state levels of factor VIII. With a single-compartment model, we found median factor VIII clearance values of 3.11 (range 1.79-7.78) x 10(3) litres/kg per h, elimination rates of 5.0-19.4 x 10(-2)/h and a median half-life of 9.9 h (range 4.8-20.0 h). Clearance and the elimination rate appeared to decline over the infusion period, as judged by the decreasing infusion rate required to maintain the target concentration of factor VIII. An economic comparison with bolus therapy, using theoretically derived bolus dosages, indicated that the potential saving was related inversely to the factor VIII half-life. Potential savings of 75% were predicted on the first postoperative day, averaging 35% over the full course of therapy.

Factor VIII↗
PubMed1996

Recommendations for the treatment of factor VIII inhibitors: from the UK Haemophilia Centre Directors' Organisation Inhibitor Working Party.

A strategy is described for the initial detection, management and elimination of factor VIII inhibitors arising in patients with congenital and acquired haemophilia A. It is suggested that children with severe haemophilia A should be screened every 3 months up to the age of 10 years for inhibitors using the Bethesda method. Factor VIII inhibitors arising in these patients should be abolished using immune-tolerance induction wherever possible. Such regimes should be started as early as possible, preferably when the inhibitor titre is < 10 Bethesda Units (BU)/ml, and should not be interrupted. High-intensity regimes are recommended for patients whose inhibitors exceed 10 BU. Autoantibodies to factor VIII giving rise to acquired haemophilia should be abolished using high-dose immunoglobulin or conventional immunosuppression. The choice of haemostatic agent for the treatment of severe bleeding should be based upon the clinical circumstances and the current inhibitor value, measured using both human and porcine factor VIII in the Bethesda assay. The past anamnestic response should also be considered when choosing treatment for minor bleeding episodes.

Blood Coagulation Factors↗
PubMed1995

Serum concentrations of von Willebrand factor and soluble thrombomodulin indicate alteration of endothelial function in inflammatory bowel diseases.

Serum concentrations of immunoreactive von Willebrand factor (vWF) and soluble thrombomodulin (TM), and vWF multimer patterns were measured to assess endothelial function in patients with inflammatory intestinal diseases. In Crohn's disease and acute infective diarrhea, vWF concentrations were significantly higher than in normal controls. In all patient groups, multimeric analysis of vWF and the concentration of serum TM were not different from normal controls. The results indicate alteration of endothelial function in inflammatory intestinal disorders. They may be compatible with the presence of localized vasculitis, but indicate that systemic endothelial destruction does not occur in inflammatory bowel disease.

Colitis, Ulcerative↗
PubMed1995

Development of resistance to activated protein C during pregnancy.

We measured activated protein C (APC) anticoagulant activity in 20 healthy women at 14-20, 28 and 36 weeks gestation, and at 1 d post-partum. Significant reductions in the mean APC sensitivity ratio (APC-SR) were observed at all stages of pregnancy studied compared with the mean APC-SR obtained for baseline measurements carried out at > 8 weeks post-partum. APC resistance was seen in 8/19 (42%) and in 11/20 (55%) women at 14-20 and 28 weeks gestation respectively. The development of resistance to APC may contribute to the increased risk of thrombosis during pregnancy.

Blood Coagulation↗
PubMed1995

The incidence of factor VIII inhibitors in the United Kingdom, 1990-93. Inhibitor Working Party. United Kingdom Haemophilia Centre Directors Organization.

Reports of all the factor VIII inhibitors arising in the United Kingdom in patients with haemophilia A during the years 1990-93 have been collated by the United Kingdom Haemophilia Centre Directors Organization. 32 new inhibitors were reported during this period, giving an average incidence of new inhibitors of 1.5 per 1000 patients registered per year. Although most occurred in patients with severe haemophilia under the age of 10, 29% occurred in patients whose VIIIC was > 3 iu/dl, and 38% in patients over the age of 10 years. The incidence of inhibitors rose during the study period, but this change was not statistically significant.

Adolescent↗
PubMed1994

Ineffectiveness of the inhibition of the main haemorrhagic metalloproteinase from Bothrops jararaca venom by its only plasma inhibitor, alpha 2-macroglobulin.

Observations that a haemorrhagic metalloproteinase (jararhagin) from Bothrops jararaca venom had less effect on platelets suspended in plasma than in washed platelet suspensions, suggested that plasma contains naturally occurring inhibitor(s) of this enzyme. By using radiolabelled jararhagin and crossed immunoelectrophoresis, we have demonstrated the binding of this enzyme to alpha 2-macroglobulin in plasma. SDS-PAGE analysis of this binding revealed the presence of radioactivity in four bands with relative molecular masses of 640, 570, 520 and 410 kDa; in addition a small amount of 47 kDa free enzyme was demonstrable. Reduced samples showed an additional non-complexed 90 kDa fragment of alpha 2-macroglobulin generated by jararhagin. These results are compatible with a model in which, upon multiple cleavages of alpha 2-macroglobulin, the enzyme becomes covalently bound to the inhibitor, and the two halves of the inhibitor become crosslinked. However, jararhagin activity was not completely inhibited even after long incubation (60 min) with a large (10-fold) molar excess of alpha 2-macroglobulin either in plasma or a purified alpha 2-macroglobulin preparation. Kinetic studies showed that inhibition was comparatively slow, although jararhagin readily cleaved alpha 2-macroglobulin in the bait region. Therefore, the ineffectiveness of the inhibition could have resulted from a low tendency of this proteinase to form covalent complexes with the inhibitor. We conclude that the pronounced haemorrhagic activity of jararhagin can be attributed to prolonged access of this enzyme to high molecular weight substrates, even in the presence of a large molar excess of alpha 2-macroglobulin.

Animals↗
PubMed1994

Arterial thrombosis in the nephrotic syndrome.

Thrombosis is a frequent cause of morbidity and mortality in patients with the nephrotic syndrome. Venous thrombotic complications are well recognized but arterial complications are rare. Thrombosis is multifactorial, and has been attributed to a hypercoaguable state due to alterations in blood levels of the various factors involved in the coagulation and fibrinolytic systems, alterations in platelet function, venous stasis, haemoconcentration, increased blood viscosity and possibly the administration of steroids. Thrombosis in general and arterial thrombosis in particular is a significant and potentially serious problem in nephrotic patients. Awareness of the condition and its pathogenesis is needed. Assessment for the risk factors is required to allow appropriate prophylactic measures to be taken.

Adult↗
PubMed1994

Properties of fibrinogen cleaved by Jararhagin, a metalloproteinase from the venom of Bothrops jararaca.

Haemorrhagic metalloproteinases from Bothrops jararaca and other venoms degrade vessel-wall and plasma proteins involved in platelet plug and fibrin clot formation. These enzymes also cause proteolytic digestion of fibrinogen which has been suggested to cause defective platelet function. Fibrinogen degradation by jararhagin, a metalloproteinase from B. jararaca, and the effect of jararhagin fibrinogenolysis on both platelet aggregation and fibrin clot formation were investigated. Jararhagin was found to cleave human fibrinogen in the C-terminal region of the A alpha-chain giving rise to a 285-290 kDa fibrinogen molecule lacking the A alpha-chain RGD 572-574 platelet-binding site. Platelet binding and aggregation of ADP-activated platelets is unaffected by this modification. This indicates that the lost site is not essential for platelet aggregation, and that the remaining platelet binding sites located in the N-terminal portion of A alpha chains (RGD 95-97) and the C-terminal of gamma chains (dodecapeptide 400-411) are unaffected by jararhagin-digestion of fibrinogen. Fibrin clot formation with thrombin of this remnant fibrinogen molecule was defective, with poor polymerization of fibrin monomers but normal release of FPA. The abnormal polymerization could be explained by the loss of one of the two complementary polymerization sites required for side-by-side association of fibrin protofibrils. Jararhagin-induced inhibition of platelet function, an important cause of haemorrhage in envenomed patients, is not caused by proteolysis of fibrinogen, as had been thought, and the mechanism remains to be elucidated.

Adenosine Diphosphate↗