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Biomedical subjects

G Savidge

Publications and source records attributed to G Savidge.

At least 19 recordsLinked to original sources
PubMed2004

Validation of a quantitative SPR assay for recombinant FVIII.

Surface plasmon resonance was employed to establish a quantitative assay for recombinant FVIII (rFVIII) products using rFVIII as standard. The anti-FVIII monoclonal antibody ESH4 was immobilized onto a carboxymethyldextran surface. A range of rFVIII concentrations were injected over the surface and the binding response enhanced by the addition of a further monoclonal antibody ESH8. Validation using National Institute of Biological Standards and Controls (NIBSC) sixth International rFVIII concentrate standard gave inter- and intra-assay coefficient of variations (CVs) of 7.5 and 3.68% respectively for ESH4-rFVIII binding alone. Enhancement of the binding signal by secondary addition of ESH8 produced inter- and intra-assay CVs of 2.75 and 1.5%. The ESH4 immobilized chip was found to retain binding capacity following regeneration for at least 75 cycles. The assay was found to be unsuitable for quantitation of plasma derived FVIII product but may prove useful for monitoring of rFVIII production.

Antibodies, Monoclonal↗
PubMed2004

Real-time quantitative PCR analysis of factor XI mRNA variants in human platelets.

Coagulation factor XI (FXI) plays an essential role in blood coagulation. A deficiency of FXI is an unusual hemorrhagic diathesis in that the bleeding tendency can be highly variable, ranging from severe deficiencies with no symptoms to mild and moderate deficiencies requiring multiple blood transfusions for hemorrhages. This variability in bleeding has been attributed to a number of factors including the presence of a novel form of FXI associated with platelets, which ameliorates the bleeding in some cases of FXI deficiency. However, the nature of this platelet FXI molecule is controversial. Hsu et al. (J Biol Chem 1998; 273: 13787-93) suggest that it is a product of normal FXI - but lacking exon V whilst Martincic et al. (Blood 1999; 94: 3397-404) were unable to detect this alternatively spliced variant using RT-PCR. In order to resolve this controversy, we have employed the highly sensitive technique of real-time quantitative RT-PCR using RNA isolated from FXI-deficient patients. Our results indicate that the platelets of both normal and FXI deficient individuals contain FXI mRNA that is identical to the mRNA found in liver. An exon V deleted splice variant was not detected. Thus the FXI message is not alternatively spliced in platelets and therefore would not be able to produce an unusual FXI protein.

Alternative Splicing↗
PubMed2004

The profibrinolytic effect of plasma thrombomodulin in factor XI deficiency and its implications in hemostasis.

Bleeding tendency in factor (F)XI deficiency may result from premature clot lysis due to insufficient thrombin activatable fibrinolysis inhibitor (TAFI) activation. Thrombomodulin (TM), upon binding to thrombin, is capable of modulating TAFI activation. In this study, we investigated the effects of plasma TM on fibrinolysis in FXI-deficient patients. A clot lysis assay showed the defective down-regulation of fibrinolysis in FXI-deficient patients as compared with normal controls. To evaluate the effects of plasma TM on fibrinolysis, a monoclonal anti-TM IgG was preincubated with plasma for 30 min. The presence of anti-TM IgG significantly prolonged the clot lysis times both in the FXI-deficient and normal plasma, indicating that plasma TM stimulated fibrinolysis. Furthermore, the presence of anti-TM IgG not only reduced protein C activation, but also increased thrombin generation and TAFI activation. The profibrinolytic effect of plasma TM was inhibited in the assay by including either a monoclonal anti-TAFI IgG or a specific TAFI inhibitor--carboxypeptidase inhibitor (CPI). Our results indicate that the impaired thrombin generation in FXI-deficient patients leads to the defective down-regulation of fibrinolysis, and that plasma TM stimulates fibrinolysis through APC pathway which inhibits TAFI activation. The profibrinolytic effect of plasma TM may contribute to the bleeding tendency observed in some FXI-deficient patients.

Adolescent↗
PubMed2000

Induction of the urokinase plasminogen activator system by oncostatin M promotes endothelial migration.

Oncostatin M (OSM) is an inflammatory cytokine produced by activated macrophages and T-lymphocytes. We have previously demonstrated that OSM-induced endothelial cell migration, unlike endothelial cell proliferation and spindle formation, is independent of basic fibroblast growth factor expression (Wijelath et al. [1997] J. Cell. Sci. 110:871-879). To better understand the mechanism of OSM-induced endothelial cell migration, this study examined the potential role of the plasminogen activator system in promoting OSM mediated endothelial cell migration. OSM stimulated increased mRNA levels of urokinase-plasminogen activator (uPA) and urokinase-plasminogen activator receptor (uPAR) in a time and dose-dependent manner. Transcriptional run-off and mRNA stability analysis demonstrated that the increase in uPA and uPAR mRNA levels was due to both increased gene transcription and mRNA stability. The increase in mRNA correlated with increased protein levels of both uPA and uPAR. This increase was reflected in elevated levels of membrane-bound plasmin activity. OSM-induced endothelial cell migration was only partially dependent on plasmin activity since incubating endothelial cells without plasminogen or, in the presence of aprotinin, resulted in suppression of endothelial cell migration, indicating that OSM promoted endothelial cell migration through both a plasmin-dependent and -independent mechanism. Our results imply a role for OSM in promoting endothelial cell migration via a plasmin-dependent pathway and a uPAR-mediated pathway. Together, these and other recent studies support a role for OSM in modulating the different phases of angiogenesis.

Cells, Cultured↗
PubMed1999

Identification of a novel mutation in a non-Jewish factor XI deficient kindred.

The role of factor XI (FXI) in blood coagulation has been clarified in recent years by descriptions of FXI-deficient patients who are prone to excessive bleeding after haemostatic challenge. We have studied a large kindred of an Italian FXI-deficient patient with a previously undescribed mutation. The propositus, a 68-year-old woman, presented with a cerebral thromboembolic event but had no history of bleeding (FXI activity 1.6 U/dl). A sensitive ELISA failed to detect FXI antigen in the propositus. Sequence analysis of the entire FXI gene revealed a TGG to TGC transversion in codon 228 of exon 7 (FXI-W228C). This missense mutation results in a Trp to Cys substitution within the third apple domain of FXI. We conclude that this novel mutation occurred in a structurally conserved region and may therefore have interfered with either chain folding and secretion or stability of FXI and was responsible for the inherited abnormality seen in this kindred. It is unclear why this kindred does not exhibit a bleeding tendency but it may correlate with a FXI-like antigen and factor IX binding activity expressed on platelets.

Aged↗
PubMed1999

Heterozygous factor XI deficiency associated with three novel mutations.

To determine the utility of single-stranded conformation polymorphism (SSCP) analysis for screening mutations in the factor XI (fXI) gene, we investigated three patients with heterozygous factor XI deficiency. DNA sequence analysis confirmed three novel mutations; a CGC --> TGC (Arg308Cys) mutation in exon 9, a GCT-->GTT (Ala412Val) mutation in exon 11 and an AGC --> AGA (Ser576Arg) mutation in exon 15. We postulated on the structural implications of these missense mutations. Our results demonstrated that genotypic analysis is a useful tool for conclusive differentiation between heterozygous factor XI deficiency and normal subjects.

Factor XI Deficiency↗
PubMed1997

Recombinant, B-domain deleted factor VIII (r-VIII SQ): pharmacokinetics and initial safety aspects in hemophilia A patients.

The pharmacokinetics of a second-generation recombinant B-domain deleted factor VIII (FVIII) preparation (r-VIII SQ) were studied in 36 patients with severe hemophilia A. In contrast to full-length recombinant FVIII, no albumin needs to be added to stabilize the final formulation of this B-domain deleted FVIII preparation. The in vivo recovery and half-life of r-VIII SQ were similar to those of plasma-derived (pd) FVIII (mean half-life of r-VIII SQ, 11.7 h). The volume of distribution and clearance were slightly, but significantly, higher for r-VIII SQ than for pdFVIII (p < 0.05). Peak plasma levels of FVIII were consistently related to the administered dose of r-VIII SQ (r = 0.94, p < 0.0001). The pharmacokinetic profile of r-VIII SQ remained essentially unchanged in a dose range of 25-100 IU/kg body weight and could be reproduced after repeated doses. r-VIII SQ was well tolerated. In conclusion, deletion of the B-domain of FVIII does not influence its in vivo pharmacokinetics.

Adolescent↗
PubMed1994

Randomized double-blind, placebo-controlled trial of twice-daily zidovudine in asymptomatic haemophiliacs infected with the human immunodeficiency virus type 1. European-Australian Haemophilia Collaborative Study Group.

In this double-blind, placebo-controlled trial of HIV-infected asymptomatic haemophiliacs, the efficacy of 2-year zidovudine therapy (1000 mg daily in two divided doses) in preventing progress of HIV infection was prospectively evaluated. Drug tolerance was also studied. 143 haemophiliacs from five European countries and Australia with p24 antigenaemia and/or CD4 cell counts of 0.1-0.4 x 10(9)/l were enrolled. The main measures of outcome were progression to AIDS, CDC group IV disease, symptomatic HIV-related disease, and a decrease in CD4+ T-lymphocyte count to fewer than 0.2 x 10(9)/l. There were no significant treatment differences in the proportion of patients progressing to AIDS, CDC group IV or symptomatic disease. Analysis of time to CD4+ counts less than 0.2 x 10(9)/l showed a non-significant trend in favour of zidovudine. Haemoglobin concentrations were less than 8 g/dl in 4% of zidovudine recipients; neutropenia was less than 0.75 x 10(9) cells/l in 5% of zidovudine recipients; alanine aminotransferase levels were greater than 10 times the upper normal limit in 3% of zidovudine recipients, but also in 4% of placebo recipients. Hence there was a very low prevalence of side-effects in haemophiliacs, despite the use of a higher zidovudine dosage than is currently widely used.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Porcine platelets contain an increased quantity of ultra-high molecular weight von Willebrand factor and numerous alpha-granular tubular structures.

Immunoelectronmicroscopy of human platelet alpha-granules reveals that von Willebrand factor (vWf:Ag) colocalizes with a small number of discrete tubular structures which appear identical to those observed within the Weibel-Palade bodies of endothelial cells. Although it is likely that tubules are composed of vWf:Ag as they are absent in severe vWD porcine platelets, their exact structural and functional nature is still unclear. In this study quantitative/qualitative analysis of vWf:Ag was undertaken in a series of platelet preparations obtained from normal pigs, normal humans and various vWD patients. Electron microscopy confirmed that normal pig platelet alpha-granules contain numerous, regularly spaced tubular structures eccentrically located and coincident with immunogold staining of vWf:Ag. In contrast, normal human platelet alpha-granules contain significantly fewer tubules (usually four to six) which are absent or reduced in number within various vWD platelet sections. Furthermore, the pig platelet lysates not only contained a full complement of multimers but also demonstrated significant intense staining of ultra-high MW material, irrespective of the presence or absence of proteolytic inhibitors. This ultra-high MW vWf appears similar to that observed within lysates prepared from endothelial cells and is susceptible to degradation to lower MW multimers. This study suggests that the tubular structures within alpha-granules and Weibel-Palade bodies may be composed of, or structurally related to, the ultra-high MW intracellular form of vWf:Ag.

Animals↗
PubMed1992

Unique expression of von Willebrand factor by type IIA von Willebrand's disease endothelial cells.

Endothelial cells (EC) were cultured from the umbilical cord of a male neonate whose mother was previously diagnosed with type IIA von Willebrand's disease (vWd). The diagnosis of type IIA vWd in the proband was confirmed by low ristocetin activity and the absence of the highest molecular weight (MW) forms of von Willebrand factor (vWf) in his platelet poor plasma. The vWf of EC cultured from the neonate's umbilical cord differed from that of control EC and the cell line EA.hy926 in two respects. Firstly, the full range of molecular weight forms was present in the patient EC lysate and, secondly, vWf:Ag expression was approximately seven-fold greater than that of control cells. Platelet lysates prepared from other affected members of the type IIA vWd family in the presence or absence of proteolytic inhibitors demonstrated a near normal vWf multimeric distribution. Resistance of these high MW forms to heat degradation was conferred by the presence of proteolytic inhibitors. Moreover, the full plasma vWf multimeric distribution could not be restored by the inclusion of EDTA. N-ethylmaleimide and leupeptin in the anticoagulant during the rapid preparation of platelet poor plasma. These findings lend support to the heterogeneous nature of type IIA vWd and has possible implications in the understanding of the intracellular processes involved in the biosynthesis and storage of the vWf macromolecular complex as well as the pathogenesis of type IIA vWd.

Blood Platelets↗
PubMed1990

Haemophilia, AIDS and lung epithelial permeability.

Lung 99mTc DTPA transfer was measured in HIV antibody-positive haemophiliacs (11 smokers, 26 nonsmokers, 5 patients with Pneumocystis carinii pneumonia (PCP]. Lung 99mTc DTPA transfer as a marker of lung epithelial permeability was measured as the half time of transfer (from airspace into blood). This half time was faster in smokers compared to nonsmokers and the transfer curve was monoexponential. In nonsmokers no difference was observed between asymptomatic HIV-positive haemophiliacs and normal subjects, with the exception of the lung bases. At the lung bases in HIV-positive haemophiliac nonsmokers the transfer was faster than in normal individuals, implying increased alveolar permeability. Pneumocystis carinii pneumonia resulted in a rapid transfer of 99mTc DTPA (mean T50 of 2 minutes) and the transfer curve was biphasic, confirming previous observations in homosexual HIV antibody-positive patients with PCP. These changes returned to a monoexponential profile by 6 weeks following successful treatment. The DTPA lung transfer study may enable clinicians to instigate therapy for PCP without the need for initial bronchoscopy and provide a noninvasive method for the reassessment of patients should further respiratory signs or symptoms develop. This method is considered to be highly cost-effective in that it obviates the use of factor VIII concentrates required to cover bronchoscopic procedures and, with its early application and ease of use as a follow-up investigation, permits the evaluation of patients on an outpatient basis, thus reducing hospital costs.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Antibody to phosphatidylethanolamine in a patient with lupus anticoagulant and thrombosis.

Most patients with lupus anticoagulant (LA) activity have coincident antibodies to a group of negatively charged phospholipids, and its is suggested that LA and anticardiolipin tests detect antibodies with overlapping specificities. Some discordance between the two assays has been described, however. One patient presenting with severe thrombotic disease (recurrent deep vein thrombosis, pulmonary embolism, inferior venocaval obstruction, myocardial infarction, and digital gangrene) showed strong LA activity in February 1987. An enzyme linked immunosorbent assay (ELISA) showed no binding to the negatively charged phospholipids cardiolipin, phosphatidylserine, and phosphatidic acid, but binding to zwitterionic phosphatidylethanolamine (PE) was demonstrated. Inhibition studies and affinity purification confirmed this finding. Interestingly, the serum did not bind to the kaolin cephalin clotting time reagent when used as antigen in an ELISA. The pathogenic significance of anti-PE antibodies and their relation to LA remains to be clarified. Further studies of the occurrence of anti-PE antibodies in patients with LA activity who have negative anticardiolipin tests are suggested.

Autoantibodies↗