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Biomedical subjects

D Hoppensteadt

Publications and source records attributed to D Hoppensteadt.

At least 55 records · Page 3Linked to original sources
PubMed1994

Fibrinolytic compromise by simultaneous administration of site-directed inhibitors of thrombin.

Newly developed synthetic and recombinant thrombin inhibitors possess strong anticoagulant effects. Despite these effects, interactions of these agents with enzymes in the fibrinolytic network result in the modulation of such proteases as t-PA, u-PA and streptokinase. The inhibitory spectrum of several thrombin inhibitors [D-Phe-Pro-Arg-H(GYKI 14166), D-MePhe-Pro-Arg-H(GYKI 14766), Boc-D-Phe-Pro-Arg-H (GYKI 14451), Ac-D-Phe-Pro-boroArg-OH (DuP 714), recombinant hirudin (r-Hir) and unfractionated porcine mucosal heparin complexed with antithrombin III (Heparin/AT-III)] was studied towards various serine proteases such as tissue plasminogen activator (t-PA), plasmin, plasminogen/streptokinase complex, urokinase and kallikrein. Aprotinin was also studied in the same systems as the thrombin inhibitors. All four tripeptide derivatives were found to inhibit t-PA, plasmin and plasminogen/streptokinase complex at micromolar concentrations (IC50: 0.57 mM-3.3 microM). Boc-D-Phe-Pro-Arg-H and Ac-D-Phe-Pro-boroArg-OH also inhibited urokinase, while Ac-D-Phe-Pro-boroArg-OH inhibited kallikrein as well (IC50: 0.15 mM-16 microM). In contrast, r-Hir and Heparin/AT-III did not inhibit any of these enzymes at millimolar concentrations (IC50 > or = 1 mM). Aprotinin inhibited plasmin, plasminogen/streptokinase complex and kallikrein at micromolar concentrations (IC50: 3.1-0.85 microM). In a rabbit thrombolysis model, where pre-formed clots are lysed by streptokinase, simultaneous administration of D-MePhe-Pro-Arg-H or Ac-D-Phe-Pro-boroArg-OH, at concentrations approximately 1 mumol/kg, i.v. resulted in complete inhibition of the fibrinolytic process. Aprotinin at 0.1 mumol/kg, i.v. produced similar inhibition. These results demonstrate that thrombin inhibitors may exert significant antiprotease actions against various fibrinolytic enzymes.

Amino Acid Sequence↗
PubMed1994

Antithrombotic agents stimulate the synthesis and modify the sulfation pattern of a heparan sulfate proteoglycan from endothelial cells.

Low molecular weight heparins, namely CY 216 and CY 222 (Sanofi/Choay); OP 622 and OP 386 (Opocrin); PK 10169 (Pharmuka); an oligosaccharide prepared from heparin by heparitinase II digestion; chemically sulfated glycosaminoglycans and polysaccharide namely Suleparoid (Syntex), Aprosulate (Luitpold-Werk); chemically modified glycosaminoglycans GAGPS and MPS (Luitpold-Werk) as well as unmodified heparin stimulate two to three fold the synthesis of a heparan sulfate with antithrombotic activity secreted by endothelial cells in culture. The stimulation is concentration dependent and specific for the endothelial cell. The [35S]-heparan sulfate synthesized in the presence of heparin and/or the tested antithrombotic agents has shown a high degree of sulfation of the iduronic acid residues as revealed by the analyses of the disaccharide products formed from the heparan sulfate by the action of bacterial heparitinases. The features of the above compounds in common with heparin are their polymeric nature and a high change density, as well as their pharmacological activities as potent antithrombotic agents "in vivo". These combined observations reinforce the proposition that the antithrombotic activity of heparin, low molecular weight heparins and the chemically modified polysaccharides could be related to the increased production of this peculiar heparan sulfate by endothelial cells.

Animals↗
PubMed1994

Role of tissue factor pathway inhibitor in post surgical deep venous thrombosis (DVT) prophylaxis in patients treated with low molecular weight heparin.

Low molecular weight heparins (LMWHs) are now considered to be the drugs of choice for prophylaxis against deep venous thrombosis (DVT) in post operative patients undergoing both general and orthopaedic surgical procedures. Despite extensive research, the exact mechanism of the antithrombotic activity of LMWHs remains unclear. These agents have been shown to activate the fibrinolytic system and to directly inhibit both the activity and the generation of factor Xa and thrombin. New evidence suggests that LMWHs also stimulate the release of endogenous tissue factor pathway inhibitor (TFPI) from the vascular endothelium. This study was designed to investigate the role of TFPI in mediating the antithrombotic activity of LMWHs. We measured the plasma levels of TFPI in a group of post orthopaedic surgery patients treated with daily subcutaneous injections of LMWH and a group of patients treated with placebo. In the placebo group (n = 25), the plasma TFPI levels were slightly elevated immediately after surgery but returned to their baseline value by the fifth post operative day. In contrast, in the group of patients treated with LMWH (n = 34), the plasma levels of TFPI increased significantly and remained elevated for up to 7 days following surgery. However, the TFPI levels in both groups showed wide patient to patient variability. These results indicate that LMWHs stimulate the release of TFPI into the bloodstream of post surgical patients. This suggests the importance of TFPI in mediating the antithrombotic activity of LMWHs.

Aged↗
PubMed1994

Low molecular weight dermatan sulfate as an antithrombotic agent. Structure-activity relationship studies.

A structure-activity relationship of low molecular weight dermatan sulfate was undertaken to understand better this new non-heparin, glycosaminoglycan-based antithrombotic agent. A dermatan sulfate prepared from bovine intestinal mucosa [average molecular weight (MWavg) 25,000], and currently in clinical trials as an antithrombotic agent, was used in this study. Dermatan sulfate was partially depolymerized using hydrogen peroxide and copper(II) as catalyst to MWavg 5600 to obtain a low molecular weight dermatan sulfate. This low molecular weight dermatan sulfate was then fractionated by gel permeation chromatography to obtain four subfractions having MWavg 7800, 5500, 4200 and 1950. The dermatan sulfate, low molecular weight dermatan sulfate and its subfractions showed substantially different optical rotations. The 1H-NMR spectroscopic analysis of dermatan sulfate samples showed some differences including increased content of GalpNAc4S6S residues and improved resolution in ring resonances for low molecular weight dermatan sulfate fractions, primarily the result of reduced molecular weight and lowered heterogeneity. Saccharide compositional analysis relied on chondroitin ABC lyase treatment followed by capillary electrophoresis. Polyacrylamide gel-based oligosaccharide mapping was also performed by treating dermatan sulfate samples with chondroitin B, AC and ABC lysases. These analyses showed increased amounts of sulfation as the MWavg decreased. In vitro bioassay showed maximum anti-Xa activity in the 4.2 kDa fraction and maximum heparin cofactor II-mediated anti-IIa activity in the 5.5 kDa fraction. The in vivo antithrombotic activity of these fractions was measured using a modified Wessler stasis thrombosis model. The 4.2 kDa fraction showed greater antithrombotic activity than the other low molecular weight dermatan sulfate fractions, dermatan sulfate, and low molecular weight dermatan sulfate. This enhanced activity may result from several structural features of the 4.2 kDa fraction including: a high content of 4,6- and 2,4-disulfated disaccharide sequences; the requirement of specific chain length; a change in the ratio of iduronic to glucuronic acid; and the presence of chondroitin ABC lyase resistant material.

Animals↗
PubMed1994

Comparative studies on the inhibitory spectrum of recombinant hirudin, DuP 714 and heparin on thrombin and factor Xa generation in biochemically defined systems.

The effect of antithrombotic drugs on the generation of serine proteases was studied in a biochemically defined system in which the prothrombin complex concentrate Konyne provided the necessary coagulation factors in the absence of plasma. The amount of thrombin and factor Xa generation was measured with a chromogenic substrate on a microcentrifugal analyzer. Furthermore, the assay was modified by supplementation with either purified antithrombin III or factor V. The synthetic peptide Ac-(D)Phe-Pro-boroArg-OH (DuP 714) was shown to be the most effective inhibitor of thrombin and also had strong inhibitor actions against factor Xa generation. Recombinant hirudin (rH) was nearly as active as DuP 714 on thrombin generation, however, it was less effective on factor Xa generation. With rH no concentration-dependent inhibition of factor Xa generation was found, i.e. over a wide range of concentration it only produced a steady inhibition of about 40-50% without further increase. The addition of AT-III to the system did not influence the action of DuP 714 or rH, but it strongly increased the inhibitory effects of unfractionated heparin (PMH) as well as of a low molecular weight heparin (LMWH) on both thrombin and factor Xa generation. The addition of factor V to the assay system did not cause any changes in the activity of all agents on protease generation.

Amino Acid Sequence↗
PubMed1994

Protamine sulfate neutralization of the anticoagulant activity of Aprosulate, a synthetic sulfated lactobionic acid amide.

Aprosulate or lactobionic acid is a highly sulfated analogue of heparin which is currently undergoing clinical trials in Europe as a potential antithrombotic drug. Aprosulate exerts a strong anticoagulant effect in plasma as a result of its interaction with heparin cofactor II. In this study, the ability of protamine sulfate to neutralize the anticoagulant activity of Aprosulate was investigated. In vitro, ex vivo, and in vivo coagulation studies were performed using various clotting assays such as the APTT, Heptest, and thrombin time as a measure of the anticoagulant activity of Aprosulate. In the first study, protamine sulfate when administered in vitro to plasma samples containing various concentrations of Aprosulate was found to effectively neutralize the anticoagulant activity of the Aprosulate in both normal human and normal monkey plasma systems. However, the relative index of neutralization of Aprosulate was assay dependent. Protamine sulfate was also found to antagonize the anticoagulant effects of Aprosulate in an ex vivo study. The ex vivo supplementation of protamine sulfate to plasma samples collected at various time intervals following the subcutaneous administration of Aprosulate to a group of primates completely neutralized the anticoagulant activity of the Aprosulate. In a third in vivo study, protamine sulfate when injected intravenously into the bloodstream of a group of primate was found to completely neutralize the anticoagulant effects of a previously administered dosage of Aprosulate. The results of these three studies clearly suggest that protamine sulfate can be used to effectively neutralize the anticoagulant activity of Aprosulate.

Animals↗
PubMed1994

Current trends in the development of anticoagulant and antithrombotic drugs.

Developments in biotechnology, synthetic chemistry, and extraction methods have contributed significantly to provide many newer antithrombotic and anticoagulant drugs. Many of these drugs exhibit mechanisms of actions distinct from heparin and oral anticoagulants. The depolymerization of heparin has resulted in the development of LMWHs. These drugs have now attained the agent of choice status for the prophylaxis of postsurgical and medical thrombotic disorders. LMWHs are now being clinically evaluated for the treatment of established thrombosis and prevention of post-acute angioplasty occlusion and reocclusion. Many newer applications of these agents will be proposed in coming years. Synthetic and recombinant antithrombin agents, such as hirudin and hirulog, have been claimed to exhibit effective anticoagulant and antithrombotic actions. The clinical data, however, are rather limited, and additional validation studies are needed. These agents, however, provide an alternate anticoagulation approach in patients who are refractory to the actions of heparin or who developed heparin-induced thrombocytopenia. Both hirudin and peptide conjugates are undergoing extensive clinical trials throughout the world in various indications. Once validated, their optimized use will provide physicians and surgeons an alternate anticoagulant approach for heparin-compromised patients. Glycosaminoglycans, such as dermatan sulfate, heparan sulfate, and other mixtures, have been developed for various indications. These drugs, however, are relatively inferior to LMWHs for the prophylaxis of thromboembolism. Although these agents have been used for phlebitis and other indications, well-designed objective clinical trials are not available at this time. Because these agents exhibit other effects, such as the effect on smooth muscle cell proliferation, these may be of some value in the control of post-percutaneous transluminal coronary angioplasty restenosis. Several synthetic analogs of heparin and related glycosaminoglycans have also been developed. One of these agents is a synthetic pentasaccharide that represents the AT-III binding site in the heparin molecule. This agent produces a strong anti-Xa effect and is devoid of any antithrombin actions. This agent is currently being developed for the prophylaxis of thromboembolism. The synthetic pentasaccharide is devoid of any effects on platelets and thus does not produce any thrombocytopenic effects. Thus it may be useful in those patients who develop thrombocytopenia and white clot syndrome. A hypersulfated lactobionic acid analog has also been developed as an antithrombotic agent. This agent was initially found to produce its antithrombotic action via HC-II. More recent data, however, show that it also releases TFPI from endogenous sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Anticoagulants↗
PubMed1994

Interleukin-2 and interleukin-6 in relation to burn wound size in the acute phase of thermal injury.

Thermal injury induces significant physiologic responses of acute inflammation, acute phase reaction and cell repair and growth, mediated by interleukins, cytokines and growth factors. To determine the relative role of interleukin-2 (IL-2) and interleukin-6 (IL-6) in the acute phase of thermal injury, 60 patients (47 men and 13 women, with average age of 37 years [1.5 to 70.0 years]) were analyzed within the first 36 hours and at five to seven days postoperatively. The patient population was categorized by percent burn (2 or 3, or both, degrees): less than 20 percent, n = 22; 20 to 40 percent, n = 18, and greater than 40 percent, n = 20. The average percent burn was 32 percent (range 4 to 95 percent). The mechanism of injury was by flame (25 instances), explosion and flame (19 instances), scald (12 instances), electric (three instances) or chemical (one instance). Twelve patients had an associated inhalation injury; 14 patients had sepsis syndrome. The overall mortality rate was 13 percent. Within 36 hours of onset of injury, IL-6 and IL-2 levels increased in proportion to the severity of the burn wound size. IL-2 levels were significantly elevated in the 20 to 40 percent burn group as compared with the greater than 40 percent group and patients in a control group (p < 0.0001). IL-6 levels increased with burn wound size and were significant only in the greater than 40 percent group (p < 0.0007). Any physiologic modulation of the thermal injury by biologic modifiers must be adapted to the extent of burn wound size and phase of injury: acute, recovery or reparative for optimal benefit and results.

Acute Disease↗
PubMed1993

Phase I--study with aprosulate, a new synthetic anticoagulant.

This paper describes the first human study with aprosulate, a new chemically synthesized anticoagulant with a defined molecular structure and a molecular weight of 2388. Twelve healthy male volunteers received subcutaneous injections of placebo on the first day followed by ascending doses of aprosulate in the range of 0.25 mg/kg to 2.0 mg/kg body weight on alternate days. Anticoagulant, pharmacokinetic and safety parameters were assessed for 48 hours after each injection. The activated partial thromboplastin time and the Heptest showed a dose-dependent increase for up to ten hours after each application. A trend towards prolongation of the bleeding time was indicated with higher doses. In general, the tolerance was good. Plasma transaminase concentrations were raised in some volunteers but returned spontaneously to normal during or after the study.

Adolescent↗
PubMed1993

Pharmacological profile of reviparin-sodium.

Clivarin (reviparin-sodium) is a homogeneous low molecular weight heparin (LMWH) as determined by the data obtained in molecular profiling studies. The limited biochemical studies carried out indicate that this LMWH has a specific potency of 124 anti-XA IU/mg and a weaker aPTT activity of approximately 30 U/mg. Assay-dependent neutralization of the in vitro effects of reviparin-sodium were 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. PF 4 only partially neutralized the effects of reviparin-sodium. Assay-dependent variations were noted in this study. In comparison with heparin, the haemorrhagic effects of reviparin-sodium were much weaker. Reviparin-sodium produced a dose-dependent antithrombotic action in both the intravenous and subcutaneous studies. This agent also showed sustained activity and better bioavailability characteristics than heparin. Reviparin-sodium exhibited a distinct biochemical and pharmacological profile that may be useful in the optimization of LMWH.

Animals↗
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↗
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

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

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↗