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Biomedical subjects

J M Walenga

Publications and source records attributed to J M Walenga.

At least 109 records · Page 6Linked to original sources
PubMed1993

Biochemical and pharmacologic profile of low molecular weight heparin (LU 47311, Clivarin).

1. Clivarin is a homogeneous LMWH as determined by the data obtained in molecular profiling studies. 2. The limited biochemical studies carried out indicated that this LMWH has a specific potency of 124 anti-Xa IU/mg and a weaker APTT activity of approximately 30 U/mg. 3. Assay-dependent neutralization of the in vitro effects of Clivarin was noted. Protamine preparations at equigravimetric concentrations effectively neutralized the APTT and TT effects; however, Heptest and anti-Xa effects were only partially neutralized. In contrast, heparin's effects were completely neutralized by this agent. 4. PF 4 only partially neutralized the effects of Clivarin. Assay-dependent variations were noted in this study. 5. In comparison to heparin, the hemorrhagic effects of Clivarin were much weaker. 6. Clivarin produced a dosage-dependent antithrombotic action in both the intravenous and subcutaneous studies. This agent also showed sustained activity and better bioavailability characteristics than heparin. 7. Clivarin exhibited a distinct biochemical and pharmacologic profile that may be useful in the optimization of this agent.

Animals↗
PubMed1993

Evaluation of hematologic alterations associated with daily administration of low molecular weight heparin (Mono-Embolex) for a 12-week period.

The long-term success rate of coronary angioplasty is only 50 to 70% due to restenosis. The pathophysiologic mechanism of this event is mainly mediated by smooth muscle cell proliferation. To some extent, it can be inhibited by heparin. The introduction of LMWHs allows for prophylaxis against restenosis on an outpatient basis, but no data are available on the long-term usage of LMWH. To investigate possible side effects, nonhuman primates received daily injections of LMWH (Mono-Embolex) over a 12-week period and the hematologic profile was assessed. There were no significant alterations of the red blood cell system. The overall WBC profile did not change, although a significant increase of granulocytes with a corresponding decrease of lymphocytes and monocytes occurred. Data from a control group suggest that these alterations are caused by chronic stress and are not drug related. Platelet count as well as platelet function tests were unaffected by this treatment. In conclusion, the long-term administration of Mono-Embolex as projected for the use in the prophylaxis of restenosis following angioplasty appears to be safe regarding hematologic parameters.

Animals↗
PubMed1993

Practical issues on the laboratory monitoring of low molecular weight heparins and related polysaccharides.

Today, we are limited by measurements of plasma factors that do not always relate to the overall pharmacodynamic response of a drug. Once the mechanism of action of the new glycosaminoglycans becomes better defined, the laboratory will be better equipped to target that biologic entity that is most appropriate for clinical measurement of effect. In the past, the PT and APTT have been the mainstay in the laboratory assessment of coagulation and monitoring heparin and warfarin. The development of new antithrombotic agents has shown us the limited sensitivity of these assays and the fact that they do not provide complete information of coagulation mechanisms. This brief article has addressed several of the key issues related to laboratory testing of glycosaminoglycans. Many questions remain; however, a practical approach incorporating these ideas in future developmental work should help in proper assay design.

Biomarkers↗
PubMed1993

Postoperative monitoring of low molecular weight heparin prophylaxis in high-risk patients.

The alterations of the laboratory assays described for heparin monitoring in low molecular weight and unfractionated heparin prophylaxis groups did not correlate with the clinical outcome. Current laboratory techniques failed to detect an increased need for a higher dose of unfractionated or low molecular weight heparin to prevent DVT in these high-risk patients. The parameters commonly associated with thrombosis, that is, decreases in protein C and AT III were correlated with an increased incidence of DVT, but there was no difference in the assay values between the low molecular weight heparin and unfractionated heparin groups. Fibrinolysis activation is known to be associated with surgery; however, our data suggest an additional activation due to low molecular weight heparin compared with the unfractionated heparin group. Most interestingly, elevated PAI levels appear to correlate with thrombosis.

Double-Blind Method↗
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

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

The effect of burn wound size on hemostasis: a correlation of the hemostatic changes to the clinical state.

The effect of burn wound size on the activation of fibrinolysis, coagulation, and contact factors was analyzed in 60 thermal injury patients. Blood samples from 47 male patients and 13 female patients, (average age 37 years; range 1.5-70 years) were collected within the first 36 hours and at 5-7 days following injury. The patient population was categorized by percentage of burn (second degree and/or third degree): less than 20%, n = 22; 20%-40%, n = 18; greater than 40%, n = 20. The average percentage of burn was 32% (range, 4%-95%). The mechanism of injury was by flame (25), explosion and flame (19), scald (12), electric (3), or chemicals (1). An associated inhalation injury was present in 12 patients. The overall mortality rate was 13% (8). Sepsis or serious infection occurred in 23% (14) of the patients. On admission, 83% of the patients had normal prothrombin times (PT) and activated partial thromboplastin times (APTT). However, specific hemostatic variables showed marked changes. Admission hemostatic markers that correlated with the severity of injury were: tissue-plasminogen activator (tPA), plasminogen activator inhibitor (PAI), D-dimer (D-di), plasminogen (Plg), proteins C and S (PrC and PrS), antithrombin III (ATIII), thrombin-antithrombin complex (TAT), kallikrein (Kal:c), kinin (Kin), C1 esterase inhibitor (C1Inh), and factor VII clotting and antigen (FVII:c, FVII:ag). These data suggest that during the early course following burn injury, thrombogenicity is increased (TAT increases) because of a decrease in ATIII, PrC, and PrS; and fibrinolysis activation (D-di increases) occurs via an increase in tPA with a p value increase in PAI.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
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↗
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

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↗
PubMed1991

Comparative studies on various assays for the laboratory evaluation of r-hirudin.

Several laboratory methods are available to measure r-hirudin, including clot-based, amidolytic, immunologic, and physicochemical techniques. The global tests, such as the PT, APTT, and Heptest, did not show an adequate response to r-hirudin in the range of 0.5 to 10.0 micrograms/ml, where full anticoagulation is achieved, as determined by animal models of thrombosis. The 10 U/ml thrombin time assay was very sensitive to r-hirudin, whereas the 10 U/ml calcium thrombin time gave a dose-dependent response from 0.15 to 10.0 micrograms/ml. Whole blood clotting assays (ACT, TEG) effectively measured r-hirudin levels up to 25 micrograms/ml. The amidolytic anti-Factor IIa assay, specific for evaluating direct thrombin inhibition, was very effective, particularly when modified to decrease the sample: thrombin ratio for higher r-hirudin concentrations. This assay may be useful in quality control, since it is biochemically defined and reagents are easily standardized. Thrombin generation assays based on synthetic substrates showed limited effect of r-hirudin; however, assays based on TAT complex and prothrombin fragment F1+2 generation showed a dose-dependent response. Immunologic methods (ELISA) are under development. Since these assays measure both complexed and noncomplexed hirudin, and since they are only sensitive to submicrogram levels, they may only be useful for the direct quantitation of absolute levels of r-hirudin but not for monitoring clinical anticoagulation. Thus, thrombin-based clotting, amidolytic, and immunologic assays can be used to evaluate and measure r-hirudin. However, optimization of each assay to respond to high and low concentrations of r-hirudin and their application to clinical monitoring, batch control, and standardization needs to be determined.

Animals↗