Werner Witt

Action of the stable prostacyclin analogue iloprost on microvascular tone and -permeability in the hamster cheek pouch.

In order to further elucidate the mechanisms involved in therapeutic effects of prostacyclin and Iloprost in peripheral ischemic disease, the actions on microvascular tone, capillary density, and increases in venular permeability induced by inflammatory mediators and by ischemia were investigated in the cheek pouch of anaesthetized Syrian hamsters using intravital videomicroscopy and--for quantification of vascular permeability--venular leakage of fluorescein-labelled dextran (FITC-D; Mw 70,000). Iloprost at the nonhypotensive, platelet aggregation-inhibiting dose of 0.5 microgram/kg/min i.v. significantly increased the diameters of arterioles and venules and the density of perfused capillaries and antagonized vasoconstriction and decrease of perfused capillary density as induced by Leukotriene D4 (LTD4; 10(-7) M). Iloprost significantly antagonized venular leakage of FITC-D induced by histamine (10(-5) M), serotonin (10(-5) M), bradykinin (10(-6) M) and reperfusion after 30 min ischemia. Topical application of Iloprost (10(-8) M), intraarterial infusion of Prostaglandin E1 (PGE1; 2.0 micrograms/kg/min), and topical Forskolin (10(-5) M) also attenuated histamine-induced venular FITC-D leakage, while topical PGE1 (10(-7) M) and i.v. infusion of Nifedipine (30 micrograms/kg + 10 micrograms/kg/min) were not effective. It is concluded, that microvascular effects of Iloprost by improvement of tissue perfusion and functional antagonism of mediator-induced tissue edema and vasospasm could contribute to therapeutic effectiveness in ischemic diseases.

Coronary thrombolysis with Desmodus salivary plasminogen activator in dogs. Fast and persistent recanalization by intravenous bolus administration.

DSPA (Desmodus salivary plasminogen activator) is a new thrombolytic agent corresponding to a natural plasminogen activator discovered in the saliva of the vampire bat Desmodus rotundus. Compared with tissue plasminogen activator (TPA), DSPA, produced in a recombinant cell line, is more fibrin cofactor dependent than TPA. Methods and ResultsThe thrombolytic properties of DSPA and TPA were compared in a canine model of copper coilinduced coronary thrombosis. All dogs received heparin 200 IU/kg IV and SC. Whereas controls did not reperfuse within 180 minutes (none of six), intravenous bolus administration of DSPA at 25, 50, and 100 μg/kg resulted in a 100% incidence (6 of 6) of recanalization within 37, 23, and 18 minutes, respectively. TPA at 63 and 125 mu;g/kg reopened the coronaries in 33% (two of six) and 50% (three of six) of cases within 40 minutes. Eighty-three percent (5 of 6) of the arteries were still patent 3 hours after 50 and 100 mu;/kg DSPA, whereas only 20% (one of five) of all coronaries originally recanalized with both doses of TPA were still open at 3 hours. Plasma levels of α2-antiplasmin decreased significantly only with 125 mu;g/kg TPA. The clearance of DSPA (2.3 to 3.5 mL · min−1 · kg−1) was lower compared with TPA (11.4 to 20 mL · min−1 · kg−1) due to a prolonged terminal half- life. ConclusionsIn a canine coronary thrombosis model, DSPA exhibited higher potency and recanalized coronary arteries faster and with a lower incidence of reocclusion than TPA. Its properties may translate into a higher efficacy in patients compared with available thrombolytic agents. The long halflife of DSPA may allow for single bolus administration in the treatment of acute myocardial infarction.

Thrombolytic properties of Desmodus (Vampire Bat) salivary plasminogen activator DSPAα1, alteplase and streptokinase following intravenous bolus injection in a rabbit model of carotid artery thrombosis

Thrombolytic properties of recombinant Desmodus salivary plasminogen activatorα1 (DSPAα1) were compared with alteplase (t-PA) and streptokinase (SK) following intravenous bolus injection in rabbits. Thrombosis was induced by a copper coil inserted in the common carotid artery. Heparin (200U/kg i.v.+i.m.) and aspirin (5mg/kg i.v.) were given in addition to the thrombolytics. Effective thrombolysis at 1, 2, 6 and 20nmol/kg DSPAai occurred in sol16,46,47 and 77 animals (controls 07), at 2, 6 and 20nmol/kg t-PA in 16, 56 and 67 animals and at 3000,10000 and 30000IU/kg SK in 24, 46, and 17 animals respectively. t-PA at 20nmol/kg significantly decreased plasma levels of fibrinogen to 72.7±4.2% (p<0.001), plasminogen to 57.1±5.1% (p<0.001) and a2-antiplasmin to 54.6±4.7% (p<0.001) of prevalue whereas DSPAα1 at 20nmol/kg only lowered α2-antiplasmin significantly to 85.3±2.5% (p<0.01). Antigen plasma levels between 30 and 120 min postdosing were higher for all doses of DSPAα1, than t-PA. DSPAai is a novel thrombolytic agent with a higher potency and clot selectivity than alteplase.

DSPA alpha — Properties of the plasminogen activators of the vampire bat Desmodus rotundus

Summary The saliva of the vampire bat Desmodus rotundus contains a family of potent plasminogen activators, which were named DSPAs after their original source (Desmodus salivary plasminogen activators). The DSPAs share a high structural homology with t-PA. Four different variants of DSPA have been discovered, called DSPA alpha1, alpha2, beta and gamma, out of which, for its unique thrombolytic properties, DSPA α1 has been selected for further development. It has a high potential to develop into a third generation thrombolytic drug. DSPA α1 is a protein with high thrombolytic potency and efficacy. Unlike all other plasminogen activators currently in use, it is almost completely fibrin specific. Furthermore, its prolonged half-life seems to warrant single bolus administration. Above all, recanalization with DSPA α1 seems to occur more rapidly and more completely and, unlike with other plasminogen activators, is sustained over prolonged time periods. Despite being a non human protein its antigenicity is low and only repeated administrations of the substance in short time intervals may non consistently produce low titers of non neutralizing antibodies. The favorable thrombolytic profile of DSPA α1 warrants studying in future thrombolytic trials.

Synergistic antiplatelet and antithrombotic effects of a prostacyclin analogue (iloprost) combined with a thromboxane antagonist (sulotroban) in guinea pigs and rats

The stable PGI2-analogue iloprost and the TXA2-receptor antagonist sulotroban were investigated for possible cooperative effects on platelet function and experimental thrombus formation in guinea pigs and rats. Iloprost and sulotroban inhibit intravascular platelet aggregation in guinea pigs and rats induced by the stable endoperoxide U 46.619 and collagen, with iloprost being the more potent and (for collagen) more efficacious drug. Combinations of both compounds show synergistic or additive effects on in vivo platelet function. Thrombus formation in rats induced by vascular damage is strongly reduced by combining doses of iloprost and sulotroban (BM 13.177) which given alone are ineffective. These results suggest a cooperative enhancement of antiplatelet and antithrombotic effects for combinations of iloprost and sulotroban. In view of disadvantages of currently used platelet inhibitors this cooperativity may offer a new approach in antiplatelet therapy.

NOVEL PLASMINOGEN ACTIVATORS FROM THE VAMPIRE BAT DESMODUS ROTUNDUS

ABSTRACT The saliva of the vampire bat Desmodus rotundus contains three size classes of plasminogen activating enzymes with a very high dependence on fibrin for biological activity. The corresponding cDNAs were cloned and it was found that four different plasminogen activating proteins exist, which are composed of domains known from the t-PA molecule. The cDNAs coding for the D. rotundus plasminogen activating enzymes were expressed in CHO cells and one form chosen for detailed in vitro and in vivo pharmacological analyses. Preliminary results show superior characteristics compared to presently available thrombolytic agents.

Effects of Iloprost on Arrhythmias and Infarct Size in Rats After Coronary Artery Ligation

Iloprost is a stable, orally active prostacyclin (PGI2) analogue with a pharmacologic profile and activity nearly identical to PGI2 [1,2]. Both PGI2 and Iloprost have been shown in a variety of experimental models to protect acutely ischemic myocardium from functional deterioration, cell enzyme leakage, and ventricular arrhythmias [3–5].

Antithrombotic Profile of Iloprost in Experimental Models of Arterial and Venous Thrombosis

Clinical benefit from treatment with Iloprost in patients suffering from throm-boembolic disorders may arise from well known properties of the drug like inhibition of platelet aggregation, vasorelaxation, cytoprotection and stimulation of the plasma fibrinolytic activity [1–3]. Some, if not all, of these properties could qualify Iloprost as a drug with antithrombotic efficacy.

Successful recanalisation of experimentally occluded coronary arteries in anaesthetised dogs with recombinant single-chain tissue-type Plasminogen activator (set-PA)

Abstract In anaesthetised closed chest dogs experimental occluding coronary thrombosis was induced by introducing a copper coil into a branch of the left circumflex coronary artery (LCX). LCX-occlusion and reperfusion after thrombolysic treatment were assessed by coronary angiography and typical ECG-signs. One hour after total LCX-occlusion vehicle alone (n=5), streptokinase (500 IU/kg/min; n=5) or single-chain tissue-type plasminogen activator (set-PA; 5000IU/kg/min; n=5) were intravenously infused. In no case spontaneous recanalisation could be observed in the control group within 150 min after onset of infarction. Streptokinase as well as sct-PA reopened the occluded LCX after an infusion period of 60 ± 23.7 min (x ± SD) and 49.5 ± 14.6 min, respectively. Compared with prethrombolytic values no significant depletion of fibrinogen, α 2 -antiplasmin, and plasminogen was observed in the dogs treated with streptokinase or single-chain tissue-type plasminogen activator.

Limitation of myocardial unperfused area and necrotic zone 24 hours and 7 days after coronary artery ligation in rats by the stable prostacyclin analogue iloprost.

Protective effects of prostacyclin (PGI2) and Iloprost in experimental cardiac ischemia are reported by several authors. However, the effects of continuous administration on the final outcome of myocardial infarction are not yet known. We investigated the effects of Iloprost on cardiac unperfused area (UA) and necrotic zone (NZ) as assessed by Evans blue perfusion and extraction and nitrobluetetrazolium staining, respectively, using osmotic minipumps for continuous intravenous drug administration. Starting 3-4 hours after left descending coronary artery-ligation (LAD-L) Iloprost was infused at doses of 0.1 microgram and 0.5 microgram X kg-1 X min-1. While the lower dose is below pharmacological effect level, the higher dose in rats slightly lowered blood pressure and effectively inhibited platelet aggregation. LAD-L in control rats resulted in UA and NZ extending to 34.2 and 16.9%, respectively, of total ventricular mass (VM) after 24 hours and 28.3 and 21.3% of VM, respectively, after 7 days. At the dose of 0.1 micrograms X kg-1 X min-1 Iloprost was ineffective in reducing UA 24 hours after LAD-L. However, at 0.5 microgram X kg-1 X min-1 Iloprost with UA and NZ of 16.3 and 8.4% of VM, respectively, after 24 hours and 8.5 and 5.2% of VM, respectively, after 7 days reduced the extension of myocardial infarction by approximately 50% after 24 hours and 70% after 7 days, as compared to controls. As assessed in unperfused ventricular tissue after LAD-L and normal myocardium of sham-operated rats following 24 hours of Iloprost infusion, myocardial tissue concentrations of Iloprost amount to approximately half of the plasma levels irrespective of LAD-L.(ABSTRACT TRUNCATED AT 250 WORDS)