Antithrombotic activity of recombinant hirudin in the rat: a comparative study with heparin

Hirudin, a potent inhibitor of blood coagulation, differs in its antithrombotic activity according to the source of isolation. It was therefore of interest to study recombinant hirudin. Hirudin was obtained by a genetic process from E. coli. Its antithrombotic action was investigated in an experimental (rat) model of venous thrombosis and was compared to heparin whose results are known. Heparin (400 micrograms/kg) and hirudin (12.5, 25 and 50 micrograms/kg) present an antithrombotic effect and limit the extension of an existing thrombus (p less than 0.05). Higher heparin dosages increase the bleeding time mean value (p less than 0.05) whereas hirudin does not. So, recombinant hirudin presents the same antithrombotic action as heparin but with very inferior dosage. This activity seems not dose-dependent and is associated to weak hemorrhagic effects.     

The comparative effects of recombinant hirudin (CGP 39393) and standard heparin on thrombus growth in rabbits

The aim of this study was to compare the ability of standard heparin and recombinant (r-)hirudin, a specific inhibitor of thrombin, to inhibit thrombus growth in a rabbit jugular vein model. Doses of standard heparin and r-hirudin equivalent in prolonging the aPTT were first identified. The ability of these doses to inhibit 125I-fibrin accretion onto preexisting thrombi was then evaluated. 0.5 and 0.75 mg/kg of standard heparin and 0.8 and 1.25 mg/kg of r-hirudin infused over 3 h produced a mean prolongation of the aPTT of 1.5 and 2 times, respectively. In saline treated rabbits 62 +/- 7 micrograms of 125I-fibrin were accreted on the pre-formed thrombi. The lower doses of standard heparin and r-hirudin produced a 125I-fibrin accretion of 44 +/- 5 and 25 +/- 4 micrograms, respectively (p less than 0.01). The two higher doses of standard heparin and r-hirudin produced a 125I-fibrin accretion of 34 +/- 4 and 17 +/- 3 micrograms, respectively (p less than 0.01). The increase in the dose of standard heparin up to 2.5 mg/kg produced a 125I-fibrin accretion of 26 +/- 3 micrograms a 58% reduction when compared with saline. The increase in the dose of r-hirudin up to 5 mg/kg produced a 125I-fibrin accretion of 12 +/- 2 micrograms, an 81% reduction when compared with saline. No further inhibition was observed when the doses of both agents were further increased. We conclude that doses of standard heparin and r-hirudin equivalent in prolonging the aPTT have a different effect on thrombus growth inhibition, r-hirudin being twice as effective as standard heparin. Exclusive inhibition of thrombin without any other inhibiting effect on blood coagulation appears to be sufficient to inhibit thrombus growth. Our results seem to be promising in view of a clinical evaluation of r-hirudin.     

Pharmacological effects of a novel recombinant hirudin, CX-397, in vivo and in vitro: comparison with recombinant hirudin variant-1, heparin, and argatroban

The novel recombinant hirudin analog CX-397 was investigated with respect to its pharmacological activity and antithrombin profiles in vivo and in vitro. In three different types of thrombosis models in rats, including stasis and thrombin-induced venous, glass surface-activated arterio-venous shunt, and ferric chloride-induced arterial thrombosis models, CX-397 and rHV-1 elicited potent antithrombotic effects, where the minimum effective doses of rHV-1 tended to be higher than those of CX-397 in the arterio-venous shunt and arterial thrombosis models. The hemorrhagic risk of CX-397 in template bleeding in rats was not higher than that of rHV-1, indicating that CX-397 is superior to rHV-1 for treating the platelet-dominant type of thrombosis. However, no differences were detected between CX-397 and rHV-1 in their effects on in vitro coagulation times and thrombin-induced platelet aggregation, suggesting the possibility that some unknown mechanisms other than simple thrombin inhibition are also involved in their antithrombotic actions.     

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.     

A comparative study of low doses of heparin and a heparin analogue in the prevention of postoperative deep vein thrombosis

The efficacy of heparin and a semi-synthetic heparin analogue as compared for the prevention of postoperative deep vein thrombosis (DVT) in a prospective, randomized trial involving 200 patients. 12 (12.5%) out of 95 patients in the heparin group developed DVT compared to 6 (6.3%) out of 94 patients who received the analogue. Serious bleeding did not occur in any of the patients in either group and the difference in the operative and postoperative bleeding was not statistically significant. In this entire series of 190 patients, wound haematoma developed in 3, and all were in the heparin group. In 50 patients (25 in each group) plasma heparin levels, kaolincephalin clotting time (KCCT) and antithrombin III (At IIII) activity were measured in the samples withdrawn before, during and immediately after surgery and also on the first postoperative day. Significantly higher mean plasma heparin levels were obtained in the pat-ients receiving the analogue than those receiving heparin. Yet there was no difference in the prolongation of the KCCT observed in the two groups when measured by the clotting assay; the analogue had greater potentiating effect on At III activity as compared to heparin; the difference being statistically significant (p < 0.005). These findings provide further evidence for our preliminary observations that the heparin analogue selectively potentiates antithrombin III activity $\text{in vivo}$ while having little effect on overall clotting. The results presented indicate that it is as effective as heparin in preventing postoperative DVT.     

Determination of the specific activity of recombinant hirudin

The anticipated importance of recombinant hirudin as an anti-thrombotic agent necessitates the development of tools for the quantification of its biological activity. A reproducible method for the determination of the specific activity of hirudin using a sensitive chromogenic assay is described. Purified recombinant hirudin proved to be close to 100% active versus thrombin. The method can also be used to determine the thrombin concentration if the hirudin concentration is known.     

Antithrombin is as effective as heparin and hirudin to prevent formation of microvascular thrombosis in a murine model

A recently published post-hoc analysis of a trial using high-dose antithrombin (AT) in septic patients (KyberSept) revealed significant reduction of lethality when no concomitant heparin was administered, whereas patients with the combination of heparin and AT did not benefit in terms of survival. Therefore, it seems feasible to study the capability of AT in prevention of microvascular thrombus formation to avoid concomitant application of heparin and AT. Using fluorescence microscopy and a light/dye-injury mouse ear model, the kinetics of thrombus formation were analyzed quantitatively in vivo upon single iv bolus of saline (control), heparin (100 IU/kg), hirudin (1 mg/kg) or AT (25, 50, 100 or 250 IU/kg) (N = 7 animals per group each). In controls, light/dye-injury induced complete thrombotic occlusion in all arterioles and venules studied. Heparin and hirudin prevented thrombotic vessel occlusion in 62% and 43% of arterioles and 11% and 28% of venules. AT-250 was found to be more effective than heparin and hirudin, because thrombus formation was completely banned in all arterioles and venules. AT-100 and AT-50 were also capable of significantly blocking thrombus formation in both arterioles and venules. In blood vessels, which finally clogged, the time for development of complete vessel occlusion was delayed after heparin, hirudin and AT-25, but in particular after AT-50 and AT-100. In conclusion, AT-mediated antithrombotic activity has been characterized in a model of phototoxicity-induced microvascular thrombosis formation, demonstrating that AT delays and prevents thrombus formation in arterioles and venules at least comparably effective as heparin and hirudin.     

A comparative study of posttraumatic stress disorder assessment under standard conditions and in the field

Little is known about the performance of clinician‐administered structured diagnostic interviews when given under variable levels of examiner training and monitoring. We sought to explore this question. We examined the performance of a self‐report questionnaire and a structured clinical interview in the assessment of post‐traumatic stress disorder (PTSD) in two community samples of war veterans. One sample was interviewed under standard conditions (N = 372) and the other under unknown and less standardized conditions (N = 420), more closely approximating ‘field conditions’. Interview results were used to predict questionnaire‐based PTSD status. Kappas, sensitivities, specificities, and positive predictive powers were moderate and of similar magnitude in both samples. Our results suggest that even under uncertain (‘field’) conditions, clinician‐administered structured interviews can produce results comparable to those produced under more tightly controlled conditions. Copyright © 2006 John Wiley & Sons, Ltd.     

A randomized double-blind study between a low molecular weight heparin Kabi 2165 and standard heparin in the prevention of deep vein thrombosis in general surgery. A French multicenter trial

The safety and efficacy of a low molecular weight heparin fragment Kabi 2165, given in the dose 2,500 anti-Xa units once daily, in preventing postoperative venous thromboembolism, was assessed against calcium heparin in the dose 5,000 IU twice daily, in a multicenter double blind randomized study. On an intention to treat basis 385 patients scheduled for major surgery were included in this study. Six patients (3.1%) out of 195 developed isotopic DVT in the Kabi 2165 group. Corresponding figures for calcium heparin was 7 patients (3.7%). There was no statistically significant difference between the two groups with respect to the bleeding variables; blood loss during operation, postoperative drainage, blood transfusion, haemoglobin and haematocrit levels; wound haematoma and haematoma at the injection sites. No patient had to undergo evacuation of wound haematoma or reoperation due to bleeding. It is concluded that one single daily injection of Kabi 2165 provides a convenient safe and effective prophylaxis against thromboembolism in general surgery.     

Anti-hirudin antibodies alter pharmacokinetics and pharmacodynamics of recombinant hirudin

Recombinant hirudin (r-hirudin) is a potent direct thrombin inhibitor with immunogenic properties. Anti-hirudin antibodies (aHAb) are detected in up to 74% of patients treated with r-hirudin for more than 5 days. aHAb may alter the pharmacokinetics and pharmacodynamics of r-hirudin. The effects of aHAb on the pharmacokinetics of r-hirudin were investigated in rats receiving r-hirudin intravenously either without aHAb (controls), 15 min after intravenous administration of non-specific antibodies or aHAb, and after pre-incubation with aHAb. When both were compared to controls and pre-treatment with non-specific antibodies, aHAb significantly altered the pharmacokinetics of r-hirudin with similar effects in both approaches: In the presence of aHAb, the volume of distribution in a steady state and total plasma clearance were diminished, while the half-life of elimination was prolonged. Both the maximum r-hirudin plasma concentration and the area under the curve were increased. In addition, r-hirudin filtration by high-flux hemodialyzer membranes (polysulfone, AN69) was investigated 1) in the absence of aHAb, 2) in the presence of non-specific mouse antibodies, and 3) in the presence of three monoclonal aHAb. In the absence of aHAb, both hemodialyzers allowed for significant r-hirudin filtration. Non-specific mouse antibodies did not markedly affect r-hirudin filtration. By contrast, all three aHAb almost completely hindered r-hirudin filtration. aHAb varied in their capacity to neutralize r-hirudin. In conclusion, aHAb markedly alter the pharmacokinetics of r-hirudin leading to r-hirudin accumulation. In the presence of aHAb, hemofiltration does not allow for rapid reduction of r-hirudin concentration. aHAb are capable of modifying pharmacodynamics of r-hirudin. Close monitoring of aHAb-positive patients treated with r-hirudin is considered mandatory.     

Affects of hirudin and heparin on the binding of new fibrin to the thrombus in t-PA treated rabbits.

The aim of this study was to compare the ability of heparin and recombinant hirudin (r-hirudin) in preventing accretion of new fibrin on thrombi during and after treatment with tissue-type plasminogen activator (t-PA) and in enhancing t-PA induced fibrinolysis in a rabbit jugular vein thrombosis model. Heparin and r-hirudin were infused at doses capable of doubling aPTT. In the fibrin accretion inhibition experiments t-PA was infused over 3 h at a dose of 0.2 mg/kg along with saline or heparin, 0.75 mg/kg or r-hirudin, 1.25 mg/kg. In rabbits treated with t-PA plus saline, heparin or r-hirudin, an accumulation of 125I-fibrinogen on the thrombi of 52.5 +/- 5.1 micrograms, 49.5 +/- 5.6 micrograms and 23.5 +/- 3.5 micrograms was observed, respectively, the difference between r-hirudin and both saline and heparin being statistically significant (p less than 0.01). The inhibition of fibrin accretion on the thrombi induced by r-hirudin persists for at least 9 h after the end of the infusion. By that time r-hirudin has been cleared from the circulation and aPTT has returned to the baseline level for at least 8 h. t-PA, 0.2, 0.4, and 1 mg/kg, infused with saline produced 34 +/- 6%, 52 +/- 5% and 79 +/- 8% lysis of pre-formed thrombi, respectively. The same doses of t-PA infused with heparin, 0.75 mg/kg, produced 32 +/- 3%, 54 +/- 5% and 78 +/- 6% fibrinolysis, respectively and infused with r-hirudin, 1.25 mg/kg, 38 +/- 3%, 57 +/- 5% and 82 +/- 8%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antithrombotic effects of recombinant hirudin in experimental angioplasty and intravascular thrombolysis

The effect of recombinant desulphatohirudin CGP 39393 (rH) on arterial thrombus formation and especially on thrombotic reocclusion after experimental angioplasty as well as after thrombolysis was investigated in rabbits. In the femoral artery thrombi were induced after endothelial damage of the vessel wall by a balloon catheter and following stasis. After removing the thrombus by angioplasty or after lysing it by streptokinase reocclusion of the artery was observed within a relatively short period of time. Subcutaneous injection of rH reduced the incidence of both primary thrombus formation and reocclusion in dependence on the dose administered. After a dose of rH of 2 mg/kg s.c. arterial thrombus formation was completely prevented and after administering 4 mg/kg s.c. thrombotic reocclusion did also not occur. Comparative studies with heparin showed that similar antithrombotic effects were only achieved at doses of 12 mg heparin/kg s.c. The results obtained suggest a clear potential of rH for prevention of thrombotic reocclusion in clinical states.     

A comparative study of standard electroencephalographic techniques and telemetry (author's transl)

The authors have used radio-telemetry to perform long duration studies and to study the variations in cerebral electrical activity. They presented a quantitative study of the distribution of paroxysmal activity in the epileptic, based on an experimental observation and confirmed as a result of the methods used. They were able to show a relationship between the severity and temporal distribution of paroxysmal activity which was confirmed statistically. Further observations were made on the distribution and onset of epileptic discharges but more detailed analysis is required before general electrophysiological conclusions can be made.     

A new therapeutic option by subcutaneous recombinant hirudin in patients with heparin-induced thrombocytopenia type II: a pilot study

We prospectively studied 15 patients suffering from acute heparin-induced thrombocytopenia (HIT) type II with and without thromboembolic events and 4 patients with anamnestically known HIT type II recurrently requiring thromboprophylaxis in order to develop new therapeutic strategies by subcutaneous recombinant hirudin administration. Patients with acute venous or arterial thromboembolism were treated with aPTT-controlled intravenous (mean: 19.3 days) followed by subcutaneous r-hirudin (mean: 22.5 days). Patients without thromboembolism were treated with subcutaneous r-hirudin (mean: 25.9 days). Four patients were readmitted to subcutaneous r-hirudin (mean: 32 days). When r-hirudin was administered subcutaneously following intravenous treatment, mean baseline (prior to the injection) and mean peak (1.5-2.5 hours after the injection) aPTT ratios were 1.1 (+/-0.2) to 1.7 (+/-0.48) and 2. 48 (+/-0.43) to 2.52 (+/-0.4) times normal value, respectively. Mean baseline and mean peak ECT ratios were 1.2 (+/-0.12) to 1.9 (+/-0. 22) and 2.2 (+/-0.25) to 2.6 (+/-0.11) times the upper normal value, respectively. When r-hirudin was initially administered subcutaneously, mean baseline and mean peak aPTT ratios were 1.41 (+/-0.25) to 1.61 (+/-00.28) and 1.88 (+/-0.26) to 2.06 (+/-0.09) times the normal value, respectively. Mean baseline and mean peak ECT ratios were 1.25 (+/-0.2) to 1.5 (+/-0.38) and 2.01 (+/-0.21) to 2.23 (+/-0.25) times the upper limit of normal, respectively. Patients who received recurrent subcutaneous r-hirudin had mean baseline and peak aPTT values of 1.5 (+/-0.35) to 1.75 (+/-0.156) and 2.0 (+/-0.33) to 2.1 (+/-0.18) times the normal value, respectively. Mean baseline and peak ECT ratios were 1.3 (+/-0.26) to 1.65 (+/-0.09) and 1.94 (+/-0.256) to 2.7 (+/-0.23) times the upper limit of normal, respectively. The overall cumulative incidence of r-hirudin antibodies was 12/19 (63%) with a significant accumulation of r-hirudin in antibody-positive patients compared to antibody-negative patients (p<0.05). No patient suffered a new thromboembolic or major bleeding event. Subcutaneous administration of recombinant hirudin provides a long-term thromboprophylaxis regimen in HIT type II patients after passivation of acute thromboembolism.     

Comparison of the effects of heparin and hirudin on thrombin binding to the normal and the de-endothelialized rabbit aorta in vitro.

The properties of heparin and hirudin to inhibit thrombin from binding to the freshly-excised rabbit aorta wall were compared in vitro. When aorta segments were incubated with 125I-thrombin (4.4 +/- 0.4 nM) in the presence of heparin or hirudin, both anticoagulants inhibited 125I-thrombin binding to the endothelium in a concentration-dependent manner (IC50: 0.1 USP U heparin/ml; 0.1 ATU hirudin/ml). Endothelium-bound 125I-thrombin was displaced by either heparin (50% liberated at 4.1 U/ml) or hirudin (0.4 U/ml). Using de-endothelialized aortas, heparin inhibited thrombin binding by the exposed subendothelium (IC50: 1.8 U/ml) whereas hirudin was without effect. Neither heparin nor hirudin was able to significantly liberate thrombin bound to the exposed subendothelium. These observations suggest that both heparin and hirudin mask the binding site on thrombin to the endothelial cell membrane. A separate site on thrombin must bind to the subendothelium because only heparin inhibits binding. Thrombin, although bound reversibly to the endothelium, is bound irreversibly to the exposed subendothelium due, probably, to reaction with endogenous extracellular antithrombin activities (e.g. antithrombin-III, protease nexin-1).     

A comparative study of the tangential-oculomotor projection.

Most of the neurons of the tangential vestibular nucleus of birds project to the controlateral oculomotor complex, but it is not known whether there is a homologous projection in mammals. In this study, horseradish peroxidase (HRP) was injected into the oculomotor nucleus of chicks and rabbits, and the distributions of labelled neurons in the target region of the vestibular complex in the two species were compared. In chicks, a large number of labelled neurons formed a continuous band of neurons located in the contralateral tangential, descending and medial nuclei. In rabbits a similar band of labelled neurons was found in the contralateral descending and medial vestibular nuclei, but most of the neurons were caudal to the incoming vestibular nerve fibers, and only a few rostral neurons were located among these fibers. Our results suggest that the tangential nucleus neurons projecting to the oculomotor nucleus may be homologous to the most lateral neurons of the neuronal band of rabbits.     

大鼠全脑缺血/再灌注模型之比较研究

目的：观察常用大鼠全脑缺血／再灌注模型在缺血及再灌注过程中ｒＣＢＦ及ＥＥＧ的变化。方法：用ｐｅｒｆｌｕｘ－３型多谱勒灌注监测测定局部脑血流量变化。用脑电图仪监测脑电波变化。结果：２ＶＯ组,３ＶＯ组与颈动脉分流组在缺血２５ｍｉｎ时ｒＣＢＦ较Ｖ４ＶＯ组下降明显。３ＶＯ组颈动脉分流组再灌注３０ｓ内ｒＣＢＦ上升较４ＶＯ组及２ＶＯ组变化较慢。