ABSTRACT
Assay conditions of a plasma-based ecarin clotting time (ECT) were evaluated and the precision of the ECT in monitoring plasma levels of r-hirudin assessed. The snake venom enzyme ecarin converts prothrombin to meizothrombin possessing only weak coagulant but strong esterase activity. In r-hirudin containing plasma samples, meizo thrombin is rapidly neutralized by r-hirudin resulting in a dose-dependent prolongation of the clotting times. Among the different assay conditions tested, addition of 50 microliters of ecarin (4 U/ml) to 100 microliters of undiluted citrate-anticoagulated plasma gave optimal results with respect to precision and reproducibility. The measuring range of the ECT performed in this way is about 0.02-5.0 micrograms/ml r-hirudin. In vitro studies performed on r-hirudin-spiked plasma samples of 50 healthy individuals demonstrate remarkably low interindividual differences in r-hirudin responsiveness as indicated by CV-values below 5% and 7% at r-hirudin concentrations between 0-3 micrograms/ml and 4-5 micrograms/ml, respectively. The specificity for r-hirudin of the ECT is further demonstrated by the strong correlation (r = 0.94) between the results of a chromogenic assay and the ECT-measured r-hirudin concentrations obtained on 67 ex vivo blood samples. Depending on the concentration of r-hirudin the ECT is sensitive to plasma levels of prothrombin. In the absence of r-hirudin the critical prothrombin concentration was found to be 20% but increasing to 60% in the presence of 2.0 micrograms/ml r-hirudin. A fibrinogen concentration of 50 mg/dl was found to be the minimal concentration independent of the r-hirudin concentration. The precision of the ECT in measuring plasma levels of r-hirudin is not influenced by treatment with heparin, aprotinin or oral anticoagulants. The data demonstrate that the ECT is a rapid and easily perfor mable clotting assay which allows accurate measurement of r-hirudin plasma levels. ECT-monitored hirudin treatment will help to establish optimal dose regimens that are more efficacious but still as safe as heparin.
Subject(s)
Antithrombins/metabolism , Hirudins/blood , Administration, Oral , Anticoagulants/administration & dosage , Antithrombins/administration & dosage , Antithrombins/adverse effects , Blood Coagulation Tests/methods , Blood Coagulation Tests/statistics & numerical data , Endopeptidases , Fibrinogen/metabolism , Hirudins/administration & dosage , Hirudins/adverse effects , Humans , In Vitro Techniques , Partial Thromboplastin Time , Prothrombin/metabolism , Recombinant Proteins/administration & dosage , Recombinant Proteins/adverse effects , Recombinant Proteins/blood , Reference Values , Reproducibility of Results , SafetyABSTRACT
Low platelet count and bleeding diathesis have been observed in patients with adrenoleukodystrophy (ALD) treated with erucic acid (22:1)-rich triglycerides ("Lorenzo's oil'). To investigate possible alterations of biophysical membrane properties, we measured platelet membrane anisotropy, which is inversely related to membrane fluidity, in 16 patients with and in 3 patients without treatment. In patients on treatment, platelet membrane anisotropy was significantly decreased. Additionally, we found increased platelet concentrations of 22:1 and compromised in vitro platelet aggregation response. The decrease of platelet membrane anisotropy is probably a main cause of bleeding diathesis. Long-term haematological side-effects must be considered in ALD patients treated with Lorenzo's oil.
Subject(s)
Adrenoleukodystrophy/blood , Blood Platelets/metabolism , Erucic Acids/analysis , Triglycerides/therapeutic use , Adolescent , Adrenoleukodystrophy/drug therapy , Adult , Anisotropy , Blood Platelets/cytology , Cell Membrane , Child , Humans , Middle Aged , Platelet AggregationABSTRACT
Five patients with various clinical and genetic phenotypes of adrenoleukodystrophy were treated with a diet enriched with glycerol trioleate and glycerol trierucate (GTE). In all patients platelet counts decreased upon the administration of GTE, but no bleeding symptoms occurred in any of the patients, and bleeding time remained normal. Pseudothrombocytopenia was excluded in all patients. Thrombocytopenia was marked (84,000-37,000/mm) in three of the patients but was fully reversible after discontinuation of GTE. Mean platelet volumes were abnormally increased in all patients. When GTE was again administered by stepwise increasing the daily dose, platelet counts showed a clearly dose-dependent decrease. Bone marrow biopsies revealed no evidence of reduced megakaryocytopoiesis. The data indicate that in patients with adrenoleukodystrophy treated with GTE platelet counts should be closely monitored because thrombocytopenia may limit the maximal daily intake of GTE.