Successful attenuation of venous thrombus growth in rabbits after the administration of a novel oral thrombin inhibitor.

Current antithrombotic compounds have several limitations in clinical practice. The present study was designed to investigate a novel orally available direct thrombin inhibitor, BSF 208791. Intravenous administration of BSF 208791 showed superior antithrombotic properties as compared with Polyethylenglycol-Hirudin (PEG-Hirudin) and low molecular weight heparin (LMWH) in a model of venous thrombosis in rabbits. The thrombus growth was 22%, 30%, 37% and 50% after BSF 208791, PEG-Hirudin. LMWH, and saline administration, respectively. Moreover, bleeding time was less affected after administration of BSF 208791 as compared with PEG-Hirudin. The oral administration of BSF 208791 resulted in adequate bioavailability and significantly reduced venous thrombus growth to 36% as compared with 60% in the saline treated rabbits. The antithrombotic effect of BSF 208791 appears to be superior to PEG-Hiridin and LMWH without affecting the bleeding time. BSF 208791 is an orally available agent that might be a promising candidate for future antithrombotic therapy.

Ancrod reduces intracerebral hemorrhage quantified in vivo by magnetic resonance imaging in rats.

BACKGROUND AND PURPOSE: Promising results of experimental and clinical stroke studies suggest that ancrod may provide an efficient therapy of brain ischemia. Because ancrod has been shown to produce rapid defibrinogenation, we investigated the effects of this agent in a rat model of intracranial bleeding using noninvasive magnetic resonance imaging (MRI). METHODS: Intracranial bleeding was induced in anesthetised rats by microinfusion of collagenase into the right striatum. Ancrod was intravenously infused for a period of 30 minutes starting 30 minutes after intrastriatal collagenase infusion. The dosages of ancrod were 0.33 IU . kg(-1) . min(-1) in one group and 1 IU . kg(-1) . min(-1) in another (total dosages were 10 and 30 IU . kg(-1), respectively). Control animals received equal amounts of vehicle solution (0.9% NaCl) only. The volume of intracerebral hemorrhage (ICH) was quantified in vivo by T1-weighted spin-echo MRI in eight consecutive coronal brain planes 24 hours after collagenase infusion. RESULTS: Plasma fibrinogen was dose-dependently diminished immediately after infusion of ancrod at dosages of 0.33 or 1 IU . kg(-1) . min(-1). Total volume of ICH was significantly (P<.05) reduced by 50% from 48 (35/57) mm(3) in vehicle-treated controls (n=17) to 24 (20/37) mm(3) in rats (n=15) infused with the lower ancrod dosage (median, 25th/75th centiles). Rats (n=15) treated with the higher dosage of ancrod had 34 (27/39) mm(3) volume of ICH, which is 29% lower compared with vehicle-treated controls (P=.05). CONCLUSIONS: Adverse side effects such as aggravation of intracerebral bleeding did not occur in ancrod-infused rats despite pronounced lowering of the plasma fibrinogen level during ongoing bleeding. In contrast, significant reductions in the volumes of ICH were observed suggesting favorable influence of ancrod in the event of intracranial bleeding in rats.

MRI study on delayed ancrod therapy of focal cerebral ischaemia in rats.

The therapeutic window for efficient post-treatment of focal cerebral ischaemia with the fibrinogen lowering agent ancrod was studied by magnetic resonance imaging (MRI) in spontaneously hypertensive rats (SHR). Ancrod or vehicle solution (0.9% NaCl) were i.v. infused (0.12 IU/kg per min) via implanted mini pumps starting 0.5, 1.5, 3 or 6 h after permanent proximal middle cerebral artery occlusion and lasting until brain mapping by multislice T2-weighted magnetic resonance imaging in vivo 24 h after middle cerebral artery occlusion. Plasma fibrinogen concentrations were measured before middle cerebral artery occlusion, before pump implantation and after magnetic resonance imaging. Total brain lesion volumes as determined by magnetic resonance imaging 24 h after middle cerebral artery occlusion were 131 +/- 36 (188 +/- 28)*, 151 +/- 39 (194 +/- 39)*, 147 +/- 44 (207 +/- 33)* and 209 +/- 60 (214 +/- 42) mm3 in rats with 0.5, 1.5, 3 and 6 h, respectively, delay of ancrod treatment (means +/- S.D., 8-11 animals/group, corresponding control groups in parentheses, *P < 0.05). Continuous i.v. ancrod infusions reduced plasma fibrinogen levels significantly (P < 0.05) in all ancrod-treated groups as compared to vehicle-treated controls until the end of the experiments 24 h after middle cerebral artery occlusion. In conclusion, significant cerebroprotection was achieved even when the onset of ancrod therapy for lowering of the plasma fibrinogen level was delayed for up to 3 h. To the best of our knowledge no drug efficacy has been reported so far with a therapeutic window of 3 h after permanent middle cerebral artery occlusion in spontaneously hypertensive rats suggesting that ancrod may provide an efficient therapy of acute human stroke.

Prevention of early reocclusion after thrombolysis of copper coil-induced thrombi in the canine carotid artery: comparison of PEG-hirudin and unfractionated heparin.

Cofactor-independent thrombin inhibitors as adjunctive treatment to thrombolysis have been found to enhance reperfusion and reduce the incidence of early reocclusion more effectively than heparins. However, all thrombin inhibitors presently available are rapidly cleared from the circulation which may cause rebound effects after cessation of treatment. To evaluate the effect of PEG-hirudin (LU 87981) a new, long acting derivative of hirudin as adjunctive treatment to rt-PA, a thrombotic occlusion of the carotid artery was induced in mongrel dogs by means of a copper coil. Vessel patency was continuously monitored with an electromagnetic flow probe. Thrombolysis of the occluded artery was induced by administration of 40 micrograms x kg-1 + 240 micrograms x kg-1 x h-1 rt-PA (low dose) or 80 micrograms x kg-1 + 480 micrograms x kg-1 x h1 rt-PA (high dose). With high dose rt-PA treatment, patency was achieved in all animals within 50 min (range 24 to 75), with low dose rt-PA treatment only in 6 out of 8 animals after 73 min (range 26 to 117). Concomitant administration of PEG-hirudin (0.3 mg x kg-1 bolus + 0.15 mg x kg-1 x h-1 infusion) increased the incidence of reperfusion in the low dose rt-PA group to 100% while the reperfusion time was shortened from 73 min in the corresponding control group to 38 min (range 20 to 75 min) in the group given PEG-hirudin (p = 0.065, Mann-Whitney U-test). The carotid artery blood flow, which rapidly declined to zero within 18 to 27 min after discontinuing low or high dose rt-PA infusions remained at a sustained level for the whole observation period of 4 h only in the group given PEG-hirudin. Only one animal reoccluded after 229 min. Unfractionated heparin (UFH) given at a dose of 0.3 mg x kg-1 bolus + 0.3 mg x kg-1 x h-1 infusion did not improve the incidence of reperfusion or lower the incidence of reocclusion. Buccal bleeding time was prolonged after high dose rt-PA treatment and after low dose rt-PA with adjunctive UFH- or PEG-hirudin treatment. Buccal blood loss was not significantly affected by either treatment. In conclusion, these experiments indicate that early reocclusion after thrombolysis can effectively be diminished by concomitant treatment with the long acting thrombin inhibitor PEG-hirudin with moderate effects on bleeding time and aPTT.

Inhibition of arterial thrombus formation in two canine models: comparison of ancrod, a fibrinogen-depleting agent, the thrombin-inhibitor r-hirudin, and the glycoprotein 11b/IIIa-receptor antagonist Ro 43-8857.

Inhibition of arterial thrombus formation by ancrod, a fibrinogen depleting agent isolated from a snake venom, r-hirudin, an inhibitor of thrombin-mediated fibrinogen cleavage, or the glycoprotein (GP)IIB/IIIa-receptor antagonist Ro 43-8857 interfering with fibrinogen binding to platelets, was evaluated in two canine models. As a marker of platelet-dependent thrombus formation, cyclic blood flow reductions (CFR) were induced in the left coronary artery (LAD) of mongrel dogs by mechanical injury of the endothelium combined with critical stenosis. In the second model CFRs were induced by thrombolysis of a copper coil-induced thrombus in the carotid artery. Blood flow rate during the reocclusion phase was used as an additional parameter of efficacy. The frequency of CFRs used a indicator of platelet aggregation and adhesion was significantly diminished by all treatments in both the carotid artery- and the LAD-model. In the LAD-model, following ancrod treatment, CFRs were correlated with plasma fibrinogen concentrations. Carotid artery blood flow after reperfusion, used as indicator of occlusive thrombus formation, rapidly declined to zero in the control group but remained at a high level after treatment with ancrod or r-hirudin. Ro 43-8857 at the selected dose improved flow rate only to a minor degree but prolonged the bleeding time from a mean value of 87.2 +/- 10.9 s (n = 24) to values > 300 s in 50% of the animals. Our results indicate that CFRs as indicator of platelet aggregation and adhesion are inhibited by either treatments. Blood flow as indicator of occlusive thrombus formation, however, is effectively improved by ancrod and r-hirudin only. Inhibition of fibrinogen binding to platelet GPIIb/IIIa receptors alone was found to be less potent antithrombotic principle in this model.

Design, synthesis and biological activity of novel rigid amidino-phenylalanine derivatives as inhibitors of thrombin.

(3S)-(Naphthalene-2-sulfonylamino)-1-[2R-(4-amidinophenyl)-1- piperidinocarbonylethyl]-2-pyrrolidinone (1a) is a potent inhibitor of thrombin with an IC50 value by 112 times lower than that of NAPAP (racemate). The selectivity versus trypsin can be improved by incorporation of substituents on the naphthyl ring. The mode of binding of the compound was determined by X-ray crystallography.

Synthesis of a homologous series of ketomethylene arginyl pseudodipeptides and application to low molecular weight hirudin-like thrombin inhibitors.

The design of low molecular weight thrombin inhibitors IIa-d (hirutonins) that bind concurrently with the enzyme's catalytic site and auxiliary "anion-binding exosite" for fibrinogen recognition is reported. A practical synthesis of the required homologous ketomethylene arginyl dipeptide inserts [Arg psi CO(CH2)nCO] (n = 1-4) corresponding to the P1-P1' scissile position of hirutonins is described. The substitution of the scissile amide function by a ketomethylene group is compatible with the enzyme active site and conferred complete plasma proteolytic stability. This modification also enhanced enzyme affinity up to 20-fold with hirutonin-4 (IIb, n = 4) displaying highest affinity (Ki = 140 +/- 20 pM). Hirutonins 1-4 exhibited potent inhibition of plasma prothrombin time (PT) and activated partial thromboplastin time (aPTT). The inhibition was biphasic and showed good correlation with the corresponding Ki. Hirutonin-2 inhibited thrombin-mediated platelet aggregation and exhibited a strong antithrombotic effect comparable to r-hirudin in an in vivo rat arteriovenous shunt model (ED15 = 1.20 mg/kg for hirutonin-2 and 1.14 mg/kg for r-hirudin). Lower molecular weight inhibitors were obtained by substituting the six native amino acid residues (Q-S-H-N-D-G), connecting the active site and the auxiliary exosite binding elements with a variable number of interening omega-aminopentenoyl units. In addition, the exosite component was reduced to seven amino acid residues (D-F-E-P-I-P-L). Incorporation of these modifications into the bifunctional format resulted in nanomolar thrombin inhibitory peptides (IIIa-c). The resulting inhibitors were studied by molecular modeling with alpha-thrombin, and the bimolecular interactions served to explain the retention of high enzyme affinity.

Primary stimuli of icosanoid release inhibit arachidonoyl-CoA synthetase and lysophospholipid acyltransferase. Mechanism of action of hydrogen peroxide and methyl mercury in platelets.

Icosanoid formation in platelets depends on the concentration of free arachidonate that is mainly liberated from membrane phospholipids by phospholipase A2. The concentration of free arachidonate is also controlled by the activities of the reacylating enzymes arachidonoyl-CoA synthetase and lysophospholipid acyltransferase. In human platelet microsomes we determined the high enzyme activities of 5.9 nmol.min-1.(10(9) platelets)-1 for the arachidonoyl-CoA synthetase and 37 nmol.min-1.(10(9) platelets)-1 for the lysophospholipid acyltransferase. The activities of these reacylating enzymes were strongly reduced by hydrogen peroxide (H2O2) and methyl mercury that are primary stimuli of arachidonate release in intact platelets. H2O2 inhibited the arachidonoyl-CoA synthetase with an IC50 of 3.3 mmol/l without affecting the lysophospholipid acyltransferase. Sulfhydryl group protection by 3-mercapto-1,2-propanediol did not overcome the inhibition but glutathione prevented the inhibition of the arachidonoyl-CoA synthetase by H2O2. This suggests that glutathione by virtue of the glutathione peroxidase reduces H2O2 rather than that it protects free sulfhydryl groups of the arachidonoyl-CoA synthetase. Methyl mercury left the arachidonoyl-CoA synthetase activity unaffected but inhibited the lysophospholipid acyltransferase activity with an IC50 of 3.4 mumol/l. The inhibition is probably evoked by the blockade of sulfhydryl groups of the lysophospholipid acyltransferase because it disappeared when 3-mercapto-1,2-propanediol was added at a concentration higher than that of methyl mercury. Thrombin as a physiological full agonist, Ca2+ less than or equal to 1 mmol/l, the calcium ionophore A23187 and phorbol 12-myristate 13-acetate (TPA) and 1-oleoyl-2-acetylglycerol as model stimuli of protein kinase C neither influenced arachidonoyl-CoA synthetase nor lysophospholipid acyltransferase. It is concluded that the inhibitory effect of H2O2 and methyl mercury on the arachidonate-reacylating enzymes arachidonoyl-CoA synthetase or lysophospholipid acyltransferase, respectively, are responsible for their capacity to stimulate icosanoid release in intact cells. Thrombin and its intracellular messengers Ca2+ and diacylglycerol do not directly affect arachidonoyl-CoA synthetase and lysophospholipid acyltransferase.

Pathophysiological role of thromboxane A2 and pharmacological approaches to its inhibition.

The formation of the proischemic and prothrombotic thromboxane A2 (TXA2) and of its functional antagonist prostacyclin is increased in patients with unstable angina and myocardial infarction. Therefore, pharmacological interventions aim at an inhibition of the synthesis or action of TXA2 without interference with the desirable effects of prostacyclin. Clinical studies currently evaluate low-dose aspirin, thromboxane synthase inhibitors, TXA2/PGH2 receptor antagonists, and a combination of the latter two principles of action. The major advantages and disadvantages of these drugs are: 1. Aspirin irreversibly inhibits TXA2 and PGH2 synthesis in platelets, but also reduces the formation of the platelet-inhibiting PGD2 and prostacyclin--even under a low-dose regimen. 2. Thromboxane synthase inhibitors increase the formation of PGD2 and prostacyclin, but also enhance the accumulation of the potent platelet agonist PGH2. 3. Competitive TXA2/PGH2 receptor antagonists selectively inhibit the action of TXA2 and PGH2 and do not interfere with the eicosanoid metabolism, but their inhibitory effect can be overcome by very high local TXA2 or PGH2 concentrations. 4. Non-competitive TXA2/PGH2 receptor antagonists do not share this drawback. Therefore, they might combine the advantage of aspirin to exert an irreversible inhibition with the specificity of a TXA2/PGH2 receptor antagonist. However, these antagonists are in the stage of experimental studies. 5. The most potent of the clinically available principles of a platelet inhibition is the combination of a thromboxane synthase inhibitor with a competitive TXA2/PGH2 receptor antagonist. Agents that combine both principles of action in one compound are also under clinical investigation.

Hydrogen peroxide and methyl mercury are primary stimuli of eicosanoid release in human platelets.

Hydrogen peroxide (H2O2) and methyl mercury induced the liberation of arachidonate and its metabolites from human washed platelets. [14C]Eicosanoids were extracted from the supernatants of [14C] arachidonate-prelabelled platelets and analysed by thin layer chromatography and radioscanning. Thromboxane B2 (TXB2), 12(S)-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) were found as stable metabolites, together with unreacted arachidonate. In the presence of dazoxiben, a shift in eicosanoid metabolism was observed towards prostaglandin E2 (PGE2), prostaglandin D2 (PGD2) and prostaglandin F2 alpha (PGF2 alpha), while in the presence of indomethacin there was a shift towards 12-HETE and unmetabolized arachidonate. The concentration pattern of those metabolites resembled that found with the physiological agonist, thrombin. H2O2 and methyl mercury also induced platelet shape change, aggregation and secretion. The EC50 values for the induction of shape change and aggregation were 27 and 850 mumol/l for H2O2 and 0.33 and 2.7 mumol/l for methyl mercury, respectively. The [3H]serotonin release required higher stimulus concentrations and amounted to 45% with 2 mumol/l H2O2 and to 16% with 3 mumol/l methyl mercury. These effects on platelet function were absent in platelets exposed to acetylsalicylic acid and prevented by indomethacin, the prostaglandin H2 (PGH2)/thromboxane A2 (TXA2) receptor antagonist, daltroban, and the functional antagonist, iloprost. In contrast, none of these drugs suppressed the formation of [14C]eicosanoids, indicating that the platelet activation by H2O2 and methyl mercury essentially requires previous PGH2/TXA2 formation. As expected, the thromboxane synthase inhibitor, dazoxiben, did not prevent, but instead potentiated the activation by H2O2 and methyl mercury through accumulated PGH2.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient concentrations and agonist potency of PGH2 in platelet activation by endogenous arachidonate.

Human platelets were prelabelled with [14C]arachidonate and stimulated with thrombin or methyl mercury. [14C]PGH2 and the more stable of the other [14C]eicosanoids formed were rapidly extracted with organic solvent cooled to -30 degrees C and analyzed by radio-TLC. TXB2 and PGH2 were also quantified by radioimmunoassay, the latter as its index metabolite PGE2. PGH2 reached its peak concentration of 12 nmol/l after 20-30 s when it amounted to approximately 2/3 of the TXB2 concentration. In the presence of the thromboxane synthase inhibitor dazoxiben, PGH2 peaked after 60 s and afterwards declined in favour of PGE2, PGD2 and PGF2 alpha. Thirty seconds after stimulation with thrombin 1 IU/ml or methyl mercury 20 mumol/l, PGH2 amounted to 35 or 28% of the cyclooxygenase products in the absence and to 66 or 63% in the presence of dazoxiben, respectively. The platelet-activating potency of PGH2 was evaluated with purified PGH2 in platelets pretreated with acetylsalicylic acid. The EC50 values of PGH2 were 0.69 and 19 nmol/l for shape change and aggregation, respectively. U 46619 produced the same effects at 4.1 and 23 nmol/l. PGH2-induced [3H]serotonin release did not exceed 25%, whereas U 46619 was able to induce approximately 50% [3H]serotonin release. Dazoxiben enhanced the aggregation induced by PGH2. Human serum albumin inhibited the aggregating effect of PGH2, suppressed the enhancing effect of dazoxiben and shifted the metabolism of PGH2 to the inhibitory PGD2. The TXA2/PGH2 receptor antagonist daltroban suppressed the agonistic effects of endogenous or added PGH2, demonstrating that the TXA2/PGH2 receptor was its site of action.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandin H2 in human platelet activation: coactivator and substitute for thromboxane A2.

(1) When platelets form TXA2 from endogeneous AA, PGH2 reaches concentrations very similar to those of TXA2 and high enough to produce strong platelet activation. Therefore, platelet activation by TXA2 appears to go along with an activation by PGH2. (2) PGH2 is a more potent stimulus of platelet shape change and aggregation than U 46619. (3) The agonism of PGH2 is limited by the formation of inhibitory prostaglandins, especially PGD2 at higher concentrations. That is why thromboxane synthase inhibitors in PRP and at a physiological HSA concentration do not augment platelet activation. (4) HSA promotes the formation of inhibitory PGD2 at the expense of agonistic PGH2.

[Madelung's lipomatosis of the neck--expression of an alcohol-induced endocrine disorder?]. / Der Madelungsche Fetthals--Ausdruck einer alkoholinduzierten endokrinen Störung?

An uncommon case of a patient with Madelung's disease (Launois-Bensaude disease, multiple symmetrical lipomatosis) is reported. Moreover, the patient suffered from alcoholic hepatomegaly, an atrophic right kidney, Dupuytren's contracture of both hands, hyperuricemia and psoriasis. The etiology of Madelung's disease is discussed.