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Nigel S Key

Publications and source records attributed to Nigel S Key.

31 records · Page 2Linked to original sources
PubMed2003

Platelet factor 4 enhances generation of activated protein C in vitro and in vivo.

Platelet factor 4 (PF4), an abundant platelet alpha-granule protein, accelerates in vitro generation of activated protein C (APC) by soluble thrombin/thrombomodulin (TM) complexes up to 25-fold. To test the hypothesis that PF4 similarly stimulates endothelium-associated TM, we assessed the influence of human PF4 on thrombin-dependent APC generation by cultured endothelial monolayers. APC generated in the presence of 1 to 100 microg PF4 was up to 5-fold higher than baseline for human umbilical vein endothelial cells, 10-fold higher for microvascular endothelial cells, and unaltered for blood outgrowth endothelial cells. In an in vivo model, cynomolgus monkeys (n = 6, each serving as its own control) were infused with either PF4 (7.5 mg/kg) or vehicle buffer, then with human thrombin (1.0 microg/kg/min) for 10 minutes. Circulating APC levels (baseline 3 ng/mL) peaked at 10 minutes, when PF4-treated and vehicle-treated animals had APC levels of 67 +/- 5 ng/mL and 39 +/- 2 ng/mL, respectively (P <.001). The activated partial thromboplastin time (APTT; baseline, 28 seconds) increased maximally by 27 +/- 6 seconds in PF4-treated animals and by 9 +/- 1 seconds in control animals at 30 minutes (P <.001). PF4-dependent increases in circulating APC and APTT persisted more than 2-fold greater than that of controls from 10 through 120 minutes (P < or =.04). All APTT prolongations were essentially reversed by monoclonal antibody C3, which blocks APC activity. Thus, physiologically relevant concentrations of PF4 stimulate thrombin-dependent APC generation both in vitro by cultured endothelial cells and in vivo in a primate thrombin infusion model. These findings suggest that PF4 may play a previously unsuspected physiologic role in enhancing APC generation.

Animals↗
PubMed2003

Analysis of individual platelet-derived microparticles, comparing flow cytometry and capillary electrophoresis with laser-induced fluorescence detection.

Platelet-derived microparticles (PMPs) formed by vesiculation during platelet activation seem to play a role in blood coagulation and in pathological disease states. Flow cytometry is currently the gold standard to characterize platelets and PMPs. Using this technique we distinguished between platelets and PMPs based on size and the presence of phosphatidyl serine (PS); PMPs were arbitrarily defined to be smaller than one micrometer and capable of forming a stable complex with fluorescently-labeled Annexin V, a protein that forms a calcium-dependent complex with PS. Further confirmation of PMP and platelet identity was done by use of fluorescently-labeled antibodies against CD41a, a glycoprotein found on the surface of both platelets and PMPs. In this report we also introduce the use of capillary electrophoresis with post-column laser-induced fluorescence detection (CE-LIF) for the analysis of fluorescently labeled platelets and PMPs. While both flow cytometry and CE-LIF can measure individual fluorescent events, only CE-LIF allowed us to calculate individual electrophoretic mobilities of activated platelets and PMPs that were then represented as distributions. A comparison between distributions suggests that PMPs have less negative mobilities. The fact that activated platelet preparations include PMPs partially obscure the interpretation of the data. While PMP and platelet number ml(-1) determined by flow cytometry is lower than the same parameter determined by CE-LIF, signal-to-noise ratio was 20 fold better for flow cytometry than for CE-LIF. This is the first time that a direct comparison between these two techniques is reported.

Blood Platelets↗
PubMed2003

Lupus anticoagulant associated with transient severe factor X deficiency: a report of two patients presenting with major bleeding complications.

Acquired factor X (FX) deficiency is rare, but has been reported in diverse disease states, including systemic amyloidosis and respiratory infections. FX deficiency associated with lupus anticoagulant (LA) and a bleeding diathesis has not been previously reported. We report two patients both of whom presented with a severe bleeding diathesis after a preceding respiratory infection due to isolated FX deficiency associated with a LA. The FX deficiency and LA were transient. We conclude that patients with LA may rarely present with severe acquired FX deficiency. This may be another mechanism whereby patients with antiphospholipid antibodies present with bleeding complications.

Antibodies, Antiphospholipid↗
PubMed2003

Congenital bleeding disorders.

Both clinical and basic problems related to the congenital bleeding disorders continue to confront hematologists. On the forefront are efforts to bring genetic correction of the more common bleeding disorders such as hemophilia A to the clinic in a safe and accessible manner. A second issue, particularly for patients with hemophilia, is the development of inhibitors-questions of how they arise and how to prevent and treat these problems that confound otherwise very successful replacement therapy and allow patients to maintain normal lifestyles. A third issue is the continuing question of diagnosis and management of von Willebrand disease, the most common congenital bleeding disorder, especially in individuals who have borderline laboratory values, but have a history of clinical bleeding. In Section I, Dr. Christopher Walsh discusses general principles of effective gene transfer for the hemophilias, specific information about viral vectors and non-viral gene transfer, and alternative target tissues for factor VIII and factor IX production. He highlights information about the immune response to gene transfer and reviews data from the hemophilia gene transfer trials to date. The future prospects for newer methods of therapy such as RNA repair and the use of gene-modified circulating endothelial progenitors are presented as possible alternatives to the more traditional gene therapy approaches. In Section II, Dr. Nigel Key focuses on inhibitor development in patients with hemophilia A. He reviews the progress in our understanding of the risk factors and presents newer information about the immunobiology of inhibitor development. He discusses the natural history of these inhibitors and the screening, laboratory diagnosis, and treatment, including the use of different modalities for the treatment of acute bleeding episodes. Dr. Key also presents information about the eradication of inhibitors by immune tolerance induction and reviews recent information from the international registries regarding the status and success of immune tolerance induction. In Section III, Dr. Margaret Rick discusses the diagnosis, classification, and management of von Willebrand disease. Attention is given to the difficulty of diagnosis in patients with mild bleeding histories and borderline laboratory test results for von Willebrand factor. She presents the value of different laboratory assays for both diagnosis and classification, and she relates the classification of von Willebrand disease to the choice of treatment and to the known genetic mutations. Practical issues of diagnosis and treatment, including clinical cases, will be presented.

Blood Coagulation Disorders↗
PubMed2002

Hepatitis C in adults and adolescents with hemophilia: a randomized, controlled trial of interferon alfa-2b and ribavirin.

Adolescents and adults with inherited disorders of coagulation have one of the highest prevalence rates of hepatitis C among known risk groups. Few data are available on the use of combination therapy with interferon and ribavirin in this population. Patients 13 years of age and older who were positive for hepatitis C virus (HCV) RNA by polymerase chain reaction and negative for human immunodeficiency virus were randomized to receive interferon alfa-2b (3 million units 3 times a week) plus ribavirin (1,000 mg/day) or interferon alfa-2b alone for 48 weeks with 24 weeks of posttreatment follow-up. Patients started on interferon alone who remained positive for HCV RNA at week 12 crossed over to treatment with interferon plus ribavirin. A total of 113 patients were treated. Thirty-seven patients were younger than 18 years. At the end of treatment, 18 of 56 (32%) treated with interferon plus ribavirin and 6 of 57 (11%) treated with interferon alone were negative for HCV RNA (P =.005). Sustained virologic response in the combination arm was 29% (16 of 56) compared with 7% (4 of 57) for those started on interferon alone (P =.027). Among adolescents younger than 18 years who were treated with combination therapy, 10 of 17 (59%) had sustained response compared with 6 of 39 (15%) of adult patients on the same regimen (P =.001). In conclusion, in this U.S. multicenter, randomized trial of therapy for HCV in patients with inherited bleeding disorders, sustained virologic response rate was significantly improved for patients treated with interferon and ribavirin compared with those started on interferon alone. Adolescents treated with combination therapy had a significantly higher sustained response than adults did on the same regimen.

Adolescent↗
PubMed2002

Coagulation inhibition for sepsis.

Following on the heels of multiple failed clinical trials of adjunctive therapeutic agents in sepsis, the positive outcome of a recent phase III study using activated protein C (APC) has led to a renewed optimism in targeted biotherapies for this syndrome. A growing body of data (both preclinical and clinical) suggests that the protection against death afforded by APC cannot be solely explained by its antithrombotic activity but rather is likely explained by its associated anti-inflammatory and profibrinolytic effects. Although a recent phase III study failed to demonstrate any protective effect of another important antithrombotic molecule, antithrombin, it is premature to conclude that the benefit observed with APC is unique among inhibitors of the coagulation system. The result of a third phase III study examining the effect of tissue factor pathway inhibitor (TFPI) in sepsis is currently awaited, and the possibility that other antithrombotic agents--and combinations thereof--have a place in the therapeutic armamentarium will undoubtedly be the topic of future studies.

Anticoagulants↗
PubMed2002

Clinical and laboratory management of the prothrombin G20210A mutation.

OBJECTIVE: To make recommendations regarding the appropriate evaluation for the prothrombin G20210A mutation, as reflected by published evidence and the consensus opinion of recognized experts in the field. DAT SOURCES: Review of the medical literature, primarily since 1996. DATA EXTRACTION AND SYNTHESIS: After an initial assessment of the literature, key points defining the condition, and review of the clinical study design, a draft manuscript was prepared and circulated to every participant in the College of American Pathologists Conference on Diagnostic Issues in Thrombophilia before the meeting. Each of the key points and associated recommendations were then presented for discussion at the conference. Recommendations were accepted if a consensus of 70% of experts attending the conference was reached. The results of the discussion were used to revise the manuscript into its final form. CONCLUSIONS: Consensus was reached on several recommendations concerning the criteria for testing for the prothrombin G20210A mutation and for the method of testing. First, a major point of consensus was that the prothrombin G20210A mutation is a significant risk factor for venous thromboembolism (VTE) and that testing should be considered in the initial evaluation of suspected inherited thrombophilia. Second, although several analytic methods are commonly used for genetic testing for the prothrombin mutation, all are generally robust and reliable. The recommendations for testing for the prothrombin mutation parallel those for the factor V Leiden mutation and include patients with a history of recurrent VTE, a first episode of VTE before the age of 50 years, a history of an unprovoked VTE at any age, thromboses in unusual anatomic sites, or an affected first-degree relative with VTE. A history of VTE related to pregnancy or estrogen use and unexplained pregnancy loss during the second or third trimesters were also considered to be indications for testing. Other scenarios remain controversial or not recommended, including general population screening.

Adult↗
PubMed2002

Hyperhomocyst(e)inemia and Thrombophilia.

OBJECTIVE: To review the role of an elevated total plasma homocysteine level (hyperhomocyst[e]inemia) in patients with venous or arterial thrombosis, as reflected by the medical literature and the consensus opinion of recognized experts in the field. DATA SOURCES: Review of the medical literature, primarily from the last 10 years. DATA EXTRACTION AND SYNTHESIS: The literature was reviewed to identify key points defining the condition, and the clinical study design of each article was examined. A draft manuscript was prepared and circulated prior to the conference to every participant in the College of American Pathologists Conference XXXVI: Diagnostic Issues in Thrombophilia. Each of the key points and associated recommendations was then presented for discussion at the conference. Recommendations were accepted if a consensus of the 70% of the experts attending the conference was reached. The results of the discussion were used to revise the manuscript into its final form. CONCLUSIONS: Consensus was reached on 9 recommendations concerning the criteria for diagnosis, the method of testing, and the approach for clinical management. A major point of consensus was that no causal role of hyperhomocyst(e)inemia in venous or arterial thrombosis is yet established. Testing methods used to measure homocysteine directly are sensitive and reliable, and provide more information than does genotyping for markers linked to abnormal plasma homocysteine.

Blood Coagulation Tests↗
PubMed2002

Possible synergy between recombinant factor VIIa and prothrombin complex concentrate in hemophilia therapy.

Recombinant factor VIIa (rFVIIa; Novoseven) is used for treatment of hemophilia patients with inhibitors. There are poorly defined differences in clinical responsiveness between individuals. Prior to licensure in the United States, rFVIIa was available through the compassionate use program, during which two patients described in this study demonstrated an excellent response. More recently, one of these individuals showed a sub-optimal response to rFVIIa. One possible explanation for different treatment outcomes was sequential therapy with prothrombin complex concentrates (PCC) followed by rFVIIa in the compassionate use program. In support of this, an in vitro test showed that this patient had an exceptionally strong response to rFVIIa when it was added to whole blood after the patient received PCC therapy. Results with other patients supported this hypothesis. With further evaluation, a therapeutic approach combining sequential PCC and rFVIIa may prove useful for treatment of bleeding refractory to either agent used alone.

Adult↗
PubMed2002

Response of factor VIII and IX-deficient blood to wild type and high membrane affinity mutant factor VIIa in an in vitro whole blood clotting assay: possible correlation to clinical outcome.

A modified form of the activated whole blood clotting time was used to evaluate response of blood from hemophilia patients to factor VIIa. Repeated assays of individuals over a one-year period showed consistency for each individual and significant difference between individuals. Four hemophilia patients with inhibitors gave low response to factor VIIa in the assay and were characterized as low or moderate clinical responders to factor VIIa therapy. Another four patients with moderate to good clinical responsiveness to factor VIIa therapy showed a strong response to factor VIIa in the assay. A factor VIIa mutant with enhanced membrane affinity showed 10- to 13-fold higher activity than wild type factor VIIa. The results may justify larger studies to determine the utility of this assay for evaluation of patient responsiveness and to set factor VIIa therapy levels.

Adolescent↗
PubMedDate not supplied

Role of the geneticist in testing and counseling for inherited thrombophilia.

Within the past decade, the identification of two mutations that are relatively prevalent among the white population (the factor V Leiden and prothrombin G20210A gene mutations) has paved the way for a number of large cohort studies that have greatly advanced our understanding of the pathogenesis of venous thromboembolism (VTE). VTE is clearly a multigenic disorder, with well-characterized examples of gene-gene and gene-environment interactions underlying its pathogenesis. Increasing numbers of patients are being referred for testing, and many more diagnoses of inherited thrombophilia are being made. The purpose of this article is to discuss the practical applications of both diagnostic testing and genetic counseling for the major inherited thrombophilias: inherited resistance to activated protein C/factor V Leiden, prothrombin G20210A mutation, protein C deficiency, protein S deficiency, and antithrombin deficiency. A description of each entity is included along with a discussion of the indications for testing, selection of the most appropriate screening test, and proper interpretation of test results. Informed consent for testing, screening of asymptomatic individuals in special circumstances (such as during pregnancy or before initiation of estrogen therapy), screening of family members, and posttest education are also addressed. This article emphasizes that these polymorphisms should be regarded as risk factors for thrombosis whose clinical expression generally depends on the coexistence of additional thrombophilic mutations or environmental conditions that provoke the development of VTE.

Environment↗