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Biomedical subjects

J Fareed

Publications and source records attributed to J Fareed.

At least 19 recordsLinked to original sources
PubMed1992

Isolation and characterization of human heparin.

Heparin was isolated from an unusually large human hemangioma that contained an elevated level of mast cells. Purification of multimilligram quantities of heparin from this tissue sample permitted a thorough examination of its structure and activity. Characterization of this human heparin included the following: one-dimensional and two-dimensional 1H-nuclear magnetic resonance spectral analysis; oligosaccharide mapping; saccharide compositional analysis; and in vitro assessment and anticoagulant activity. Oligosaccharide mapping and nuclear magnetic resonance spectroscopy showed that this human heparin is structurally similar to porcine intestinal mucosal heparin but distinctly different from bovine lung heparin. This human heparin also has substantially more in vitro anticoagulant activity than either of these pharmaceutical heparins.

Animals↗
PubMed1992

Neutralization of the antithrombotic effects of heparin and Fraxiparin by protamine sulfate.

In general, the in vitro anti Xa activity of low molecular weight heparins is neutralized to a lesser degree than the anti Xa activity of unfractionated heparin. To determine whether these differences occur in vivo, a rabbit stasis thrombosis model and a rat laser-induced thrombosis model were utilized. In the laser model, a similar degree of neutralization of the antithrombotic activity of heparin and Fraxiparin was obtained. However, in the stasis thrombosis model, significant antithrombotic activity of Fraxiparin remained after equigravimetric protamine administration. Ex vivo APTT, thrombin time, Heptest, amidolytic anti Xa and anti IIa assays were performed. A coefficient (r = .806) was obtained for the correlation of Heptest activity to antithrombotic effect in the stasis thrombosis model, while the coefficients obtained for the other tests ranged from .152-.570. However, after neutralization by protamine, the thrombin time exhibited the highest correlation coefficient (r = .685) between ex vivo activity and residual antithrombotic effect. Since Fraxiparin retains antithrombotic activity after protamine administration, clinical benefit may be observed for this low molecular weight heparin as compared to unfractionated heparin after neutralization.

Animals↗
PubMed1992

Ex vivo activity of heparin is not predictive of blood loss after neutralization by protamine.

To study whether the ex vivo activity of heparin and Fraxiparin correlates to and predicts the extent of blood loss induced by the heparins (pre- and post neutralization by protamine), a rat tail transection model and a rabbit ear bleeding model were used. In the rat model heparin (2 mg/kg i.v.) significantly prolonged the bleeding time, while this dose of Fraxiparin had no effect. In the rabbit ear blood loss model, heparin (2 mg/kg i.v.) produced significant increases in blood loss while Fraxiparin (2 mg/kg i.v.) produced approximately 30% of the blood loss induced by heparin. Equigravimetric protamine reduced the heparin-induced blood loss by approximately 50%, however, significant blood loss, thrombin time and Heptest activity remained. Heparin and Fraxiparin (3 mg/kg s.c.) did not cause any increased bleeding. While, all activities of heparin were completely neutralized by protamine, the Heptest activity of Fraxiparin was resistant to neutralization. The ex vivo activity of heparins after neutralization by protamine does not correlate to the extent of blood loss which suggests it may not be necessary to neutralize all ex vivo activities of the heparins to baseline values to be assured that blood loss is reversed.

Animals↗
PubMed1992

The thrombolytic potency of LMW-heparin compared to urokinase in a rabbit jugular vein clot lysis model.

Since the beginning of the clinical use of low molecular weight (LMW) heparins their thrombolytic or profibrinolytic potency has been a matter of controversial discussions. Regarding this problem, the aim of our study was to test a LMW-heparin (Sandoparin) in an in vivo model comparing its lytic activity to unfractionated heparin and urokinase at different doses. For this purpose a newly developed short-term rabbit jugular vein clot lysis model was developed. Urokinase infused at doses of 3300, 6600 and 10,000 U/kg to control animals for one hour showed a clear dose-dependent clot lysis. Test animals were injected with a bolus of 0.5 mg/kg of LMW-heparin followed by a constant infusion of either 0.5, 1.0 or 2.0 mg/kg for one hour. A similar dose-dependent effect was observed for LMW-heparin as for urokinase. Unfractionated heparin did not exhibit a dose-dependent lytic activity in this model. No lysis was found in rabbits treated with saline. These findings suggest that the LMW-heparin tested exhibits a dose-dependent in vivo lytic activity which can be compared to clinically effective doses of urokinase, and that this activity is not present with unfractionated heparin.

Animals↗
PubMed1992

Influence of recombinant hirudin and unfractionated heparin on thrombin and factor Xa generation in extrinsic and intrinsic activated systems.

Using biochemically defined conditions on a fast kinetic centrifugal analyzer the effect of recombinant hirudin (rH) and unfractionated heparin (UH) on thrombin and factor Xa generation was investigated. Diluted fibrinogen deficient human plasma was incubated with increasing concentrations of the anticoagulants and protease generation was initiated either by extrinsic (EA; thromboplastin/calcium chloride) or intrinsic (IA; ellagic acid/cephaloplastin/calcium chloride) activation of the coagulation process. Generation of thrombin or factor Xa was measured continuously by amidolytic assays using the specific chromogenic substrates Spectrozyme TH and Spectrozyme FXa. By means of calibration curves for thrombin and factor Xa the IC50 values for the inhibition of the proteases were calculated. It was found that rH and UH were nearly equally effective in inhibiting both the thrombin and factor Xa formation after IA, whereas in EA system rH produced a stronger inhibition on thrombin generation than UH, which in general showed a more pronounced effect after intrinsic than after extrinsic activation. The results suggest that, with regards to thrombin and factor Xa generation, rH does not exhibit a much higher activity than UH. This may be an expression that thrombin-mediated positive feedback-reactions are not influenced by rH as strongly as expected when using a highly specific and selective thrombin inhibitor. Furthermore, it can be concluded that protease generation assays may be useful in the characterization of anticoagulants/antithrombotics.

Blood Coagulation↗
PubMed1992

Inhibition of factor X, factor V and prothrombin activation by the bis(lactobionic acid amide) LW10082.

The minimum concentrations of heparin, dermatan sulfate, hirudin, and D-Phe-Pro-ArgCH2Cl required to delay the onset of prothrombin activation in contact-activated plasma also prolong the lag phases associated with both factor X and factor V activation. Heparin and dermatan sulfate prolong the lag phases associated with the activation of the three proteins by catalyzing the inhibition of endogenously generated thrombin. Thrombin usually activates factor V and factor VIII during coagulation. The smallest fragment of heparin able to catalyze thrombin inhibition by antithrombin III is an octadecasaccharide with high affinity for antithrombin III. In contrast, a dermatan sulfate hexasaccharide with high affinity for heparin cofactor II can catalyze thrombin inhibition by heparin cofactor II. A highly sulfated bis(lactobionic acid amide), LW10082 (Mr 2288), which catalyzes thrombin inhibition by heparin cofactor II and has both antithrombotic and anticoagulant activities, has been synthesized. In this study, we determined how the minimum concentration of LW10082 required to delay the onset of intrinsic prothrombin activation achieved this effect. We demonstrate that, like heparin and dermatan sulfate, LW10082 delays the onset of intrinsic prothrombin activation by prolonging the lag phase associated with both factor X and factor V activation. In addition, LW10082 is approximately 25% as effective as heparin and 10 times as effective as dermatan sulfate in its ability to delay the onset of prothrombin activation. The strong anticoagulant action of LW10082 is consistent with previous reports which show that the degree of sulfation is an important parameter for the catalytic effectiveness of sulfated polysaccharides on thrombin inhibition.

Antithrombin III↗
PubMed1992

Gradient polyacrylamide gel electrophoresis for determination of molecular weights of heparin preparations and low-molecular-weight heparin derivatives.

The M(r) values of pharmaceutical heparins and low-molecular-weight (LMW) heparin derivatives were examined as part of a collaborative study to develop methods for their characterization. Standard methods of M(r) determination rely on gel permeation high-performance liquid chromatography (HPLC). We report the use of gradient polyacrylamide gel electrophoresis (PAGE) to determine the M(r) values of pharmaceutical heparins and LMW heparin derivatives. This approach offers certain advantages over the HPLC method. Gradient PAGE analysis was performed in parallel, on multiple samples, with the same standard curve. HPLC was performed serially. Gradient PAGE gave higher resolution than HPLC, and thus, a mixture of easily obtained standards was used in place of individual standards for the construction of a standard curve. Heparin and various LMW heparin samples were analyzed by both gradient PAGE and conventional gel permeation HPLC methods. The number-average M(r), weight-average M(r), and polydispersity were examined by both techniques and found to be similar. This study demonstrates that gradient PAGE analysis is a sensitive method for the determination of the M(r) values of heparin and LMW heparin.

Carbohydrate Sequence↗
PubMed1992

Hemostatic abnormalities in total artificial heart patients as detected by specific blood markers.

We retrospectively evaluated the hemostatic system of 13 patients during implantation (2 to 35 days) of the Jarvik 7-70 total artificial heart (TAH). Although all patients were clinically manageable while on the TAH, 5 had excessive generalized bleeding. After the heart transplant procedure, 2 patients had neurological events and 1 patient, thrombosis of the leg. While the patients were supported by the TAH, the routine coagulation assays (prothrombin time, activated partial thromboplastin time, fibrinogen, factor assays, and platelet count) showed slight abnormalities but no correlation to hemorrhagic or thrombotic events. In contrast, plasma and cellular activation markers, which are highly sensitive and specific for hypercoagulability, fibrinolysis, or platelet activation, revealed activation in all patients. Most striking was the marked activation of the fibrinolytic system (p less than 0.05 to 0.001). Correlations of individual patient data compared with the average TAH group response could be made between excessive enhancement of fibrinolysis (increased D-dimer and tissue plasminogen activator and decreased plasminogen activator inhibitor) and bleeding. A hypercoagulable state (increased fibrinogen and thrombin-antithrombin complex and decreased antithrombin III and protein C), decreased fibrinolysis (decreased tissue plasminogen activator and D-dimer), activated platelets (increased thromboxane B2), or combinations of these were associated with thrombosis. The hemostatic activation returned to normal 1 day after removal of the TAH. These data suggest that the patient with a TAH requires more sophisticated laboratory monitoring and individualized treatment for excessive fibrinolysis, hypercoagulable state, or platelet activation to avoid thrombotic and hemorrhagic complications.

6-Ketoprostaglandin F1 alpha↗
PubMed1992

Reduction of plasma levels of prothrombin fragments 1 and 2 during thromboprophylaxis with a low-molecular-weight heparin.

In a randomized double-blind placebo-controlled study, plasma levels of prothrombin fragment 1 and 2 and total fibrin/fibrinogen degradation products were measured preoperatively and on days 1, 3, 5 and 7 postoperatively in 131 patients undergoing total hip replacement. Patients received a subcutaneous injection of either a low molecular weight heparin (Logiparin) or placebo once daily. Postoperative deep vein thrombosis was diagnosed by bilateral phlebography 7 to 10 days after operation. In the placebo group postoperative levels of prothrombin fragments 1 and 2 and total fibrin/fibrinogen degradation products were significantly higher in patients with postoperative thromboembolic complications, whereas in the low-molecular-weight heparin group no statistical differences were observed. Compared with placebo the administration of a low-molecular-weight heparin was associated with a significant reduction in the levels of prothrombin fragments 1 and 2 and total degradation products. Our observations suggest that the postoperative thrombin generation is moderated by thromboprophylaxis with Logiparin.

Adult↗
PubMed1992

Tracheal and bronchial cartilaginous rings: warfarin sodium-induced calcification.

Progressive calcification of the cartilaginous rings (CCR) of the trachea and bronchi has been observed in patients undergoing prolonged prophylactic anticoagulant therapy with warfarin sodium. The purpose of this study was to validate the relationship of warfarin sodium and CCR, as well as to present the appearance and sex and age distribution of the normal degenerative CCR seen in the elderly. Chest radiographs were scrutinized for evidence of CCR in 92 patients who underwent warfarin sodium therapy and in 105 patients used as a control group. CCR was classified as not present (scored as 0), subtle (scored as 1), and extensive (scored as 2). In the warfarin sodium study group, 47% of patients (43 of 92) exhibited level 1 or level 2 CCR. This proportion was 19% (20 of 105) in the control group. The difference was statistically significant (P less than .001). A significant positive correlation (P less than .001) was also present between the duration of warfarin sodium therapy and increased levels of CCR.

Aged↗
PubMed1992

Drug-induced alterations of hemostasis and fibrinolysis.

The hemostatic and fibrinolytic systems contribute significantly to the overall pathophysiologic status of a patient in a given clinical setting. Drug modulation of these systems plays a crucial role in the facilitation of the therapeutic effects but may also produce bleeding or thrombotic disorders. Many drugs appear inert; they can, however, modulate both the hemostatic and fibrinolytic systems. Such effects depend on several factors, however, but are significant enough to be recognized for the optimal care of patients. Therefore, it is recommended that the hemostatic and fibrinolytic systems should be routinely monitored during drug delivery.

Anticoagulants↗
PubMed1991

In vitro studies on thrombin generation in citrated, r-hirudinized and heparinized whole blood.

The generation of thrombin in citrated, r-hirudinized and heparinized whole blood (final concentrations 10, 25, 50 micrograms/ml) was studied in the presence or absence of various activators. Whole blood from healthy volunteers was activated either by glass or dextran sulfate (contact activation; CA) as well as by thromboplastin/calcium chloride (extrinsic activation; EA) and by ellagic acid/cephaloplastin/calcium chloride (intrinsic activation; IA) and incubated 10 (CA, EA, IA) and 30 (CA) min at 37 degrees C. After the incubation period plasma levels of prothrombin fragment 1 + 2 (F1 + 2) and thrombin-antithrombin III complex (TAT) were measured utilizing ELISA methodology. After EA or IA no blood clotting occurred in all r-hirudinized samples and in heparinized blood at the highest concentration used. Despite inhibition of clotting F1 + 2 levels were increased both in r-hirudinized and in heparinized blood. However, in blood anticoagulated with heparin F1 + 2 levels after EA, IA and especially after CA were markedly lower than in r-hirudinized blood. Furthermore, in r-hirudinized blood an increase of TAT levels was found. The enhancement of F1 + 2 and TAT levels by r-hirudin was concentration-dependent and was lower in the higher r-hirudin concentration. The results indicate that in r-hirudinized whole blood significant amounts of thrombin can be generated which may elicit thrombin-mediated feedback mechanisms.

Blood Coagulation↗
PubMed1991

Structural features of dermatan sulfates and their relationship to anticoagulant and antithrombotic activities.

Dermatan sulfate is a polydisperse, microheterogeneous sufated copolymer of N-acetyl-D-galactopyranose and idopyranosyluronic acid that is currently under clinical investigation as a new antithrombotic agent. The structure and activity of two pairs of dermatan sulfates, isolated from bovine and porcine mucosa, were studied. One dermatan sulfate from each species demonstrated high in vivo antithrombotic activity in the rat vena cava assay. The in vitro anticoagulant activity of each dermatan sulfate was determined using activated partial thromboplastin time (APTT), thrombin time (TT) (5 units), calcium thrombin time (CaTT) (5 units), Heptest, anti-factor Xa and anti-factor IIa antithrombin assays and heparin cofactor II amidolytic assays. The coagulation-based assays gave the best correlation to in vivo antithrombotic activity. The physical and chemical properties of each dermatan sulfate were determined using 1H-NMR and 13C-NMR spectroscopy, molecular weight determination, potentiometric titration, chemical degradative analysis, chondroitin lyase degradative analysis and oligosaccharide mapping. These analyses indicated that the major difference between dermatan sulfates from a particular species having high and low in vivo antithrombotic activity was their iduronic acid content. The relation between increased iduronic acid content and increased in vivo antithrombotic activity may be the result of the conformational flexibility of this residue.

Animals↗
PubMed1991

Components of coagulation and fibrinolysis during thrombosis prophylaxis with a low molecular weight heparin (Enoxaparin) versus Dextran 70 in hip arthroplasty.

In a prospective randomized study heptest, thrombin-antithrombin complexes (TAT), D-dimer, and t-PA:ag were analysed pre- and postoperatively in 206 consecutive patients undergoing hip arthroplasty during thromboprophylaxis with either a LMW heparin (Enoxaparin) or Dextran 70. Deep vein thrombosis (DVT) developed in 6 of 102 (6%) Enoxaparin and in 21 of 104 (20%) Dextran patients diagnosed by bilateral phelobography. In the Enoxaparin group heptest showed a significant increase from the pre- to the postoperative level opposed to a significant decrease in the Dextran group. Postoperative levels of TAT, D-dimer, and t-PA:ag were significantly increased in both groups, however, TAT was significantly higher in patients in the Dextran group than in the Enoxaparin patients. D-dimer was significantly higher in Dextran patients with DVT postoperatively compared with patients without DVT. No differences concerning TAT or t-PA:ag were observed between patients with and without DVT in any of the groups.

Adult↗
PubMed1991

Potential use of recombinant hirudin as an anticoagulant in a cardiopulmonary bypass model.

Recombinant (r) hirudin is a potent thrombin-specific inhibitor derived from the natural hirudin of the leech (Hirudo medicinalis). We have studied the efficacy of r-hirudin compared with heparin in a canine model of cardiopulmonary bypass operations. Two administration regimens were used for r-hirudin: group 1, 1.0 mg/kg intracardiac bolus then intravenous bolus at 30 minutes (n = 10); and group 2, 1.0 mg/kg intracardiac bolus with 1.25 +/- 0.04 mg.kg-1.h-1 intravenous infusion (n = 8). Group 3 was given an intracardiac bolus of heparin, 1.66 mg/kg (n = 9). Aspiration of blood from the chest cavity revealed no significant difference between the three groups. Measurement of fibrin deposits in the pump line filter revealed higher amounts in the r-hirudin groups (p = 0.02). Decreases in platelets, fibrinogen, and hematocrit due primarily to hemodilution were the same in each group. The bleeding time assay showed less prolongation for r-hirudin than for heparin (p less than 0.001). No antagonist for r-hirudin was used; however, due to its short half-life all coagulation variables returned to baseline within 30 minutes after cardiopulmonary bypass. Because r-hirudin lacks effect on platelets, is a poor immunogen, does not require a plasma cofactor, and may not require an antagonist, it may provide an alternative anticoagulant to heparin in cardiopulmonary bypass. Additional studies are, however, needed to optimize the dose and to evaluate other clinical aspects of r-hirudin.

Animals↗
PubMed1991

Laboratory monitoring of the clinical effects of low molecular weight heparins.

Despite a clinical prophylactic efficacy of low molecular weight heparins (LMWHs) for 24 hrs after a single subcutaneous administration, the routine laboratory tests (anti-Xa, anti-IIa, Heptest, APTT which show a reliable in vitro dose-response) exhibit no ex vivo response after 6 hours. In addition, the values obtained in these assays do not correlate with clinical efficacy or bleeding side effects. With therapeutic doses of LMWHs, a proportionately higher effect was noted in these tests including, in addition, thrombin generation, Heptest-Hi, and thrombin time assays. However, the relevance of these assays to the clinical efficacy/toxicity of LMWHs remains unclear since they do not relate to the total pharmacodynamic effect. For example, protamine neutralization, adjunct drug treatment and a patient's own predisposing factors which contribute to the hemostatic balance may not be reflected in these assays. These observations point to the limitations of the available laboratory tests for monitoring LMWHs. In order to find a more sensitive means to detect the effects of LMWH, assays for specific molecular markers of coagulation and fibrinolysis activation were evaluated. Alterations in the levels of thrombin-antithrombin complex, t-PA, total degradation products and D-dimer assays were observed over a 7-10 day LMWH treatment period. Prothrombin fragment F1+2, modified antithrombin, PAI and fibrinogen degradation products were not significantly effected. The association of the changes observed in these markers to the mechanism of action of LMWH or to the efficacy of the treatment, however, remains to be determined.

Animals↗