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Biomedical subjects

J Fareed

Publications and source records attributed to J Fareed.

At least 343 records · Page 19Linked to original sources
PubMed1983

Molecular markers of hemostatic disorders: implications in the diagnosis and therapeutic management of thrombotic and bleeding disorders.

With current technological advances, it is now possible to measure in less than 50 microL of plasma picomolar amounts of circulating products of platelet activation, products of protease activation related to coagulation and fibrinolytic pathways, and prostaglandin metabolites formed during a physiologic or pathologic process. Most of these markers, which circulate in blood in nanogram or picogram amounts per milliliter during or after pathologic activation, provide pertinent information on the status of a patient in terms of specificity and early detection, and will be of crucial value in the diagnosis of hemostatic defects and the management of newer antithrombotic drugs that cannot be monitored by currently available assays. Currently, 125I- and 3H-based simple radioimmunoassays are available for platelet factor 4, beta-thromboglobulin, fibrinopeptide A, B beta 15-42 related peptides, thromboxane B2, and the prostaglandins 6-keto-PGF1 alpha and PGE2. Nonisotopic methods such as enzyme-linked immunosorbent assays and fluoroimmunoassays are being developed. Serotonin and ADP, products of platelet activation, are measurable by liquid-chromatographic, immunoenzymatic, and spectrophotofluorometric methods. Analytical methods for fibrin split products (fragments D and E) and serine protease inhibitor complexes such as thrombin-antithrombin-III, factor Xa-antithrombin-III, and kallikrein-C1-esterase are also being developed. We have evaluated all of these methods and found them to be very sensitive to those components of endogenous activation of the hemostatic system listed above.

Blood Coagulation Disorders↗
PubMed1983

Newer synthetic peptide substrates in coagulation testing: some practical considerations for automated methods.

More than 100 chromogenic and fluorogenic peptide substrates are now available for the evaluation of coagulation and related parameters. Many of these substrates exhibit undesirable physical properties, such as insolubility, surface adsorption, and interaction with endogenous plasma proteins. Some of these substrates are capable of inhibiting serine protease generation during activation in the global assay. In order to develop synthetic chromogenic substrates with desirable physical and biochemical characteristics, modified amino acids, such as CHG, CHT, and Nleu, have been utilized. Similarly, to provide a favorable molecular environment to facilitate enzyme and synthetic substrate interactions, various molecular manipulations, such as the introduction of bulky groups, is helpful in developing substrates for protein Ca and C1-esterase. Substrates for Factor Xa, CH3-O-CO-CHG-Arg-pNA (bovine Xa, Km 2.5 X 10(-4) M; human, Km 3.5 X 10(-4) M); thrombin, H-D-CHT-Ala-Arg-pNA (bovine thrombin, Km 3 X 10(-6) M; human thrombin, Km 6 X 10(-6) M); plasmin, H-D-Nleu-CHT-Lys-pNA (human plasmin, Km 2.2 X 10(-5) M) were found to have identical or superior biochemical characteristics to the earlier substrates. These newer substrates were found to be more soluble (greater than 5 X 10(-4) M) in physiologic buffer, less susceptible to autoamidolysis at reaction conditions, and did not produce opacity of the test solution in final concentrations of 5 X 10(-4) M. Comparable results on normal and pathologic plasma samples were obtained in various laboratory assays that utilize currently available substrates for Factors Xa and IIa, kallikrein, and plasmin (R = greater than 0.9). We propose that prior to the application of a new synthetic substrate in a given assay, a careful biochemical and physical screening of the substrate, the assay conditions, and the interaction of substrates with plasma proteins is highly desirable.

Blood Coagulation Factors↗
PubMed1983

Newer avenues in the monitoring of antithrombotic therapy: the role of automation.

In the future, we may find that antithrombotic therapy provides its major effects other than by Factors Xa and IIa inhibition, in which case a panel of assays may be of clinical use to determine how a given patient is responding to therapy. All methods discussed previously for direct factor assays, global tests, or specific factor inhibition can be modified for synthetic substrates. With instruments such as the IL Multistat III centrifugal analyzer, which has detection capabilities for visible light, fluorescence and light scatter, it will be possible to panel profile synthetic substrate-based assays, immunologic assays (for example, platelet release products or circulating complexes of enzyme-inhibitor, such as thrombin-AT III) and possibly platelet aggregations/luminescence in one rotor. The field of coagulation is rapidly expanding in the development of newer tests to measure newly discovered proteins (protein C), development of new drugs and therapeutic regimens, and incorporating immunologic and enzymologic technologies and clinical chemistry standardization and quality control practices. Throughout this period of growth, automation has been in the forefront and is playing an ever-increasing role in every old and new aspect of coagulation evaluation. We are aware of the advantages that accompany any automated device over manual techniques, so there should be much hope and expectation for the new hemostasis and thrombosis laboratory.

Administration, Oral↗
PubMed1983

Diagnostic efficacy of newer synthetic-substrates methods for assessing coagulation variables: a critical overview.

With the introduction of synthetic substrates, many newer methods have been developed for testing coagulation parameters. Some of these methods are used in clinical settings, and many have been evaluated for their diagnostic efficacy in various coagulation disorders. Clinical chemistry laboratory instrumentation has been used to accommodate these methods. Commercially available kits for antithrombin III, heparin, plasminogen, alpha 2-antiplasmin, and factor X are used by many laboratories. Individual reagents have also become available and are being used to develop assays for routine diagnostic use. The development of suitable standards is rapidly underway, and their availability will facilitate adoption of these methods by hospital laboratories. Many of the synthetic-substrate-based assays that have been introduced for routine diagnostic purposes have been published recently. Here, we provide an overview of the newer amidolytic methods for the measurement of certain coagulation variables.

Anticoagulants↗
PubMed1982

Studies on a highly active anticoagulant fraction of high molecular weight isolated from porcine sodium heparin.

We have studied heparin fractionation using gel filtration and ion-exchange chromatographic methods. The starting material was commercial grade porcine mucosal sodium heparin (PSH). The fractionation was monitored employing synthetic substrates for assaying both antithrombin (with H-D-Phe-Pip-Arg-pNA ; S-2238) and anti-FXa (with Bz-Ileu-Glu-Gly-Arg-pNA ; S-2222) activities. The resulting fractions were evaluated in different amidolytic and coagulation methods used to determine heparin potency by comparison with PSH. By gel filtration of PSH on Ultrogel Aca 54, both strong anti-FXa and antithrombin activities were associated with the fractions eluted in the high molecular weight range (MW congruent to 20 x 10(3)). These fractions also had potent anticoagulant action when assayed by conventional clotting methods. PSH was also subjected to fractionation by an ion-exchange technique (DEAE-Sephacel) with increasing salt molarity. The patterns for antithrombin and anti-FXa activities were again closely related, if not identical. Four fractions were usually distinguished, with respectively negligible, intermediate, high and very high activities when compared to PSH. The very highly active fraction (HAF), approximately 15% by weight, was eluted at high salt molarity (greater than 0.8 M NaCl). On a weight basis its anticoagulant activity was congruent to 2-3 times that of PSH as determined by amidolytic as well as clotting methods. Intravenous injection of HAF to rabbits and dogs (1.0 and 2.5 mg/kg) produced a much stronger anticoagulant response than PSH, also showing an effect which persisted for a longer duration.

Animals↗
PubMed1982

Ionic and non-ionic contrast media interaction with anticoagulant drugs.

Normal and pathologic human plasmas were incubated with radiographic contrast media, heparin, Dextran-40 and saline. Renografin-60 produced a strong anticoagulant effect and the clotting times were significantly prolonged; the addition of heparin resulted in greatly elevated thrombin time. No such prolongation was noted with Dextran-40. P-297, ioxaglic and ioxithalamic acids also showed similar anticoagulant properties. When dogs were injected with contrast media and heparin, the overall anticoagulant effect lasted for more than 6 hours, while contrast media or heparin effect remained for a short period of time. Clinical significance of contrast media interactions with anticoagulant drugs is discussed.

Animals↗
PubMed1982

Contrast media induced serotonin release in human blood.

Several contrast media were tested for their ability to release serotonin from whole blood. Renografin-60, Hypaque M-75, Vascoray and Conray were incubated with human blood at 37 degrees C for 60 min. Platelet-poor plasma was analysed for serotonin using a high performance liquid chromatographic technique. Seven non-ionic contrast media were similarly incubated and serotonin levels determined. Ionic contrast media induced a greater release of serotonin compared with non-ionic ones. The amount of serotonin was not proportional to iodine concentration in blood. These results suggest that hypertonic solutions of contrast media produce a physical injury to platelets causing them to release their granular contents.

Adult↗
PubMed1981

Automation of plasma antithrombin III assays.

We have developed automated assays for antithrombin III for use with the Gilford 3500 and the Multistat Microcentrifugal Analyzer. The assays are two-stage kinetic-rate methods and involve use of human thrombin and the chromogenic peptide substrate S-2238. The reagents are prepared in-house from commercially available components. Both automated methods have good precision and results correlate well with both an established chromogenic substrate assay and an immunological assay. The automated assays offer the advantages of speed, sensitivity, high throughput, and low reagent consumption and are useful for both routine work and high-volume testing in clinical studies and screening programs.

Antithrombin III↗
PubMed1981

Role of splenic red pulp in endotoxin-induced disseminated intravascular coagulation.

As an extension of our studies on vascular responses to endotoxemia, we evaluated sequential ultrastructural lesions of splenic red pulp and correlated these lesions with coagulation changes observed in rhesus monkeys following infusion with endotoxin either as a single bolus (10 mg. per kg.) or at a continuous rate of 10 mg. per kg. per hour for periods up to 16 hours. Controls included monkeys infused with Ringer's lactate solution. Progressive reactions of the splenic cords included increased phagocytic activity of macrophages in association with aggregation and degranulation of platelets and prominent fibrinous deposits characteristically abutting basement membranes of endothelial and reticular cells. The sinuses demonstrated endothelial damage, platelet-fibrin microthrombi obstructing interendothelial slits, and severe engorgement with entrapment of erythrocytes by tactoids of fibrin. The thrombotic lesions of the red pulp developed earlier than similar lesions in hepatic sinusoids, and they were accompanied by progressive thrombocytopenia and disseminated intravascular coagulation. The findings suggest that the unique microcirculation of the spleen is an early target and trigger of endotoxin-induced microthrombosis. It is proposed that phagocytosis of endotoxin by splenic phagocytic cells and associated inflammatory events result in disruption of reticular cells and endothelium leading to massive microthrombosis with breakdown of the splenic filter. In addition, rapid activation of coagulation mechanisms in the red pulp as well as liver sinusoids may promote the development of thrombocytopenia and disseminated intravascular coagulation in endotoxic shock.

Animals↗