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Biomedical subjects

D Hoppensteadt

Publications and source records attributed to D Hoppensteadt.

At least 73 records · Page 4Linked to original sources
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↗
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

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↗
PubMed1991

An objective perspective on recombinant hirudin: a new anticoagulant and antithrombotic agent.

Leeches have been in medical use for many years. Hirudin, the anticoagulant obtained from the medicinal leech has been purified, characterized and can now be produced by recombinant (r) technology. R-hirudin is a potent inhibitor of thrombin and is therefore a potentially valuable anticoagulant and antithrombotic drug. This article reviews the current status of r-hirudin in this role and compares the pharmacokinetics, mechanism of action and clinical efficacy of this agent with heparin. The methods available for laboratory assessment and clinical monitoring of r-hirudin and the possible ways of antagonizing its effects are also discussed. Finally, the potential clinical applications of r-hirudin are outlined, although further laboratory and clinical studies, together with a fall in the cost of this compound are required before r-hirudin can be more widely accepted as an anticoagulant and antithrombotic agent.

Amino Acid Sequence↗
PubMed1991

Biochemical evidence for a relative lack of inhibition of thrombin formation by nonionic contrast media.

An in vitro study was done to investigate the thrombogenic potential of nonionic contrast media. Whole blood from 18 healthy volunteers was mixed with ionic contrast medium (diatrizoate, ioxaglate), a non-ionic contrast medium (iohexol), or saline (the control) and incubated in glass and plastic test tubes. Levels of prothrombin fragment 1 + 2 (F1 + 2), thrombin-antithrombin III complex (TAT), and antithrombin III (AT III) were measured. Evidence showed increased thrombin formation in glass tubes compared with that in plastic tubes, a finding in concordance with the known association between contact with glass and increased activation of coagulation. F1 + 2 and TAT levels were significantly increased in the nonionic mixtures compared with such levels in ionic mixtures (P less than or equal to .05). Control mixtures showed little or no overall increased thrombin formation by F1 + 2 and TAT levels compared with nonionic mixtures. These findings suggest an inhibition of thrombin generation by ionic contrast media in vitro and a relative lack of such inhibition by iohexol.

Antithrombin III↗
PubMed1991

Laboratory assays for the evaluation of recombinant hirudin.

Several laboratory methods are available to measure the anticoagulant activity of recombinant hirudin (r-hirudin), a potent thrombin inhibitor. These assays include clot-based, amidolytic, immunologic and physicochemical techniques. Although r-hirudin, like heparin, is an effective anticoagulant, the mechanism of action of the two agents is different. Thus it is not surprising that the global tests, such as the prothrombin time (PT), partial thromboplastin time (APTT) and the Heptest (Haemachem, Inc., St. Louis, Mo., USA), do not show adequate responses to r-hirudin. In the range of 0.5-10.0 microgram/ml, where full anticoagulation is achieved, as determined by animal models of thrombosis, these assays show little to no prolongation of the time to clot. In order to find a more suitable assay system, modifications of the above assays were evaluated. The diluted APTT and diluted Heptest showed linear concentration-dependent responses to lower levels of r-hirudin with an enhanced sensitivity than that of the classical assays. On the other hand, the diluted thrombin time was too sensitive. Whole-blood clotting assays, ACT and thrombelastograph, 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. This assay may be useful in quality control since it is biochemically defined, and reagents are easily standardized. The relevance of the results of the anti-IIa assay to clinical conditions, however, remains to be determined. Thrombin generation assays have limited value in monitoring the anticoagulant effect of r-hirudin since the effect of thrombin inhibition by r-hirudin on coagulation feedback mechanisms, and thus the effect on thrombin generation, appears to be minimal. Immunologic methods such as ELISA and RIA are under development, but they may only be useful for the direct quantitation of absolute levels of r-hirudin and not for monitoring the clinical anticoagulant action. Furthermore, these assays are only sensitive to sub-microgram/ml levels. Therefore, thrombin-based clotting and amidolytic assays may at present be the best choice for evaluating the functional, clinical antithrombotic effects of r-hirudin.

Blood Coagulation↗
PubMed1991

Some objective considerations for the neutralization of the anticoagulant actions of recombinant hirudin.

Recombinant hirudin (r-hirudin) is currently under development as an anticoagulant for use in surgery, therapeutic anticoagulation, disseminated intravascular coagulation and other pathologic states involving the generation of thrombin. Circulating levels of r-hirudin as an antithrombotic agent range from 2 to 20 micrograms/ml (0.1-1.0 mg/kg) as determined in an animal model of stasis thrombosis. In order to establish a relationship between the r-hirudin circulating level and bleeding, we utilized a rabbit ear blood loss model. r-Hirudin did not produce any loss of blood at dosages up to 20 micrograms/ml i.v. (1.0 mg/kg). When the circulating levels were maintained at 20 micrograms/ml for periods of up to 3 h, no increase in blood loss was observed. At 50 and 100 micrograms/ml initial circulating levels (2.5 and 5.0 mg/kg) a dose-dependent increase in the blood loss was observed which was equivalent to that observed with 1.25 and 2.5 mg/kg i.v. heparin. Such levels of r-hirudin are not expected in clinical usage. In contrast to heparin, the anticoagulant actions of r-hirudin were not neutralized by protamine sulfate, platelet factor 4, other polycationic agents and heparinase. In our studies, the blood loss induced by greater than 2.0 mg/kg i.v. dosages of r-hirudin in an animal model was neutralized by the administration of an activated prothrombin complex concentrate at 25 U/kg. In a similar experimental setting, r-factor VIIa was also partially effective. These studies suggest that r-hirudin anticoagulation may not require neutralization, since bleeding effects are not observed at effective antithrombotic dosages in individuals with normal hemostatic status.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Experimental and clinical validation of the prophylactic antithrombotic effects of a low molecular weight heparin (enoxaparin).

Several LMWHs are currently available for commercial use. The development status of each of these products in the area of prophylaxis, therapeutics, and other indications is given in Table 4. Enoxaparin and Fraxiparin appear to be the most developed LMWHs in both the surgical and medical areas. Many well-designed clinical trials have been carried out for different clinical indications with both of these products. As demonstrated in both experimental and clinical settings, the prophylactic antithrombotic efficacy of Enoxaparin is distinct from other LMWHs. This agent has provided consistently impressive clinical results. However, at comparable dosages, other products have exhibited safety or efficacy profiles different from those of Enoxaparin. It is therefore justified to comment that the clinical performance of each LMWH is characteristic of only that particular agent. It can be stated that, provided proper developmental approaches, these agents will more than likely be the drugs of choice for the prophylaxis and therapy of thrombotic disorders. On the other hand, inadequate basic knowledge may result in the development of products with unknown safety or efficacy profiles whose introduction in clinical medicine may become related to problematic situations.

Hemorrhage↗
PubMed1991

Non-heparin glycosaminoglycan-derived drugs: a biochemical and pharmacologic perspective.

The developments in the area of glycosaminoglycan derived drugs can be summarized in the following: 1. Currently available glycosaminoglycan-derived drugs represent a first generation of clinically useful agents. At present these agents are not optimized and their basic and clinical pharmacology is poorly understood. 2. Most of these agents represent mixtures of different types of glycosaminoglycans. They can be purified to isolate their active components and perhaps many new drugs may be developed from the existing products. 3. Chemical derivatization and fractionation methods can be used to obtain more defined products. These products will be developed for specific clinical indications. 4. Each glycosaminoglycan derived product should be considered as an individual drug and should be developed separately. 5. Many semisynthetic and synthetic analogs of glycosaminoglycans will be introduced for various clinical indications.

Animals↗