Binding and lysing of blood clots using MRX-408

RATIONALE AND OBJECTIVES: A thrombus-specific ultrasound contrast agent, MRX-408, has been developed recently. This agent consists of phospholipid-coated microbubbles with a ligand capable of targeting the GPIIb/IIIa receptor, thereby allowing the microbubbles to bind with thrombi rich in activated platelets. In vitro and in vivo animal experiments have been conducted to examine imaging enhancement and sonothrombolysis using this agent compared with a nontargeted agent. METHODS: For clot binding, blood-smeared slides were incubated with microbubbles and examined under a light microscope. Change in backscatter signals from the blood clots after binding was examined by both an ultrasound scanner and two single-element transducers arranged in a transmitter-receiver pair. For clot lysis, either 1-MHz or 20-KHz ultrasound was used to enhance the lysing effects of MRX-408 with or without urokinase. RESULTS: Evidence of binding was demonstrated under a microscope. In vitro experiments showed that the "acoustic signature", or properties, of blood clots changed after binding. Clots became more echogenic and nonlinear. In vivo fundamental ultrasound imaging confirmed that as a result of binding, blood clots were more visible, the area of detection was improved, and shadowing behind clots was more noticeable. Under 1-MHz ultrasound and 30 minutes of treatment, lysis efficiency reached 34% with MRX-408, whereas there was no visible clot lysis with saline. CONCLUSION: The results of these preliminary studies show that as a contrast agent, MRX-408 enhanced clots under ultrasound imaging and facilitated sonothrombolysis with or without thrombolytic drugs.     

Thrombin binds to soluble fibrin degradation products where it is protected from inhibition by heparin-antithrombin but susceptible to inactivation by antithrombin-independent inhibitors

BACKGROUND: Thrombolytic therapy induces a procoagulant state characterized by elevated plasma levels of fibrinopeptide A (FPA), but the responsible mechanism is uncertain. METHODS AND RESULTS: Washed plasma clots were incubated in citrated plasma in the presence or absence of tissue plasminogen activator (t-PA), and FPA generation was monitored as an index of unopposed thrombin activity. FPA levels are almost twofold higher in the presence of t-PA than in its absence. This primarily reflects the action of thrombin bound to soluble fibrin degradation products because (a) there is progressive FPA generation even after clots are removed from t-PA-containing plasma, and (b) clot lysates produce concentration-dependent FPA generation when incubated in citrated plasma. Using thrombin-agarose affinity chromatography, (DD)E and fragment E but not D-dimer were identified as the thrombin-binding fibrin fragments, indicating that the thrombin-binding site is located within the E domain. Heparin inhibits thrombin bound to fibrin degradation products less effectively than free thrombin. In contrast, D-Phe-Pro-ArgCH2Cl, hirudin and hirugen inhibit free thrombin and thrombin bound to fibrin degradation products equally well. CONCLUSIONS: Thrombin bound to soluble fibrin degradation products is primarily responsible for the increase in FPA levels that occurs when a clot undergoes t-PA-induced lysis. Like clot-bound thrombin, thrombin bound to fibrin derivatives is protected from inhibition by heparin but susceptible to inactivation by direct thrombin inhibitors. These findings help to explain the superiority of direct thrombin inhibitors over heparin as adjuncts to thrombolytic therapy.     

Clot formation by group A streptococci

Group A streptococci of several different M serotypes can cause human plasma to clot in nutrient-poor media. Addition of glucose to the medium prevents clot formation. Once formed, clots are stable for several days and can be lysed on addition of exogenous streptokinase or urokinase. Clot lysis can also be achieved by addition of glucose to a clot containing wild-type group A streptococci but not clots containing an isogenic mutant in which the ska gene was inactivated.     

A bleeding model in rabbits demonstrate fresh clot selectivity for a genetically engineered variant of tissue-type plasminogen activator and for streptokinase

The way in which three thrombolytic agents, tissue-type plasminogen activator (t-PA), streptokinase (SK) and a genetically engineered variant of t-PA composed of the second kringle and the protease domain (K2P), cause the dissolution of haemostatic plugs of differing ages was investigated in a novel rabbit model. Standardized incisions were made on the rabbit ear and the wounds were left to heal for 0.5 h or 24 h, before the thrombolytic agents were infused. In the absence of heparin, t-PA showed little discrimination between clots of different ages (36% and 28% lysis of the 0.5 h and 24 h wounds, respectively). In contrast, K2P and SK showed a pronounced fresh clot selectivity since they were significantly more effective in lysing fresh clots than old ones (68% and 4% lysis for K2P and 72% and 36% for SK, respectively). In the presence of heparin the potency of t-PA on fresh clots was considerably increased whilst the effect on old clots was not affected, a fresh clot selectivity for t-PA (64% lysis of fresh clots, 24% lysis of old clots) was thus effected. Heparin did not significantly affect the fresh clot selectivity of K2P or SK, although lysis of old clots was increased (from 4% to 36%) when it was given together with K2P. Furthermore, heparin did not affect the time to onset of bleeding nor was the bleeding time prolonged by its addition. The bleeding time observed for t-PA (20-25 min) was markedly shorter than that found for K2P or SK (40-50 min).(ABSTRACT TRUNCATED AT 250 WORDS)     

Thrombolytic and pharmacokinetic properties of a recombinant chimeric plasminogen activator consisting of a fibrin fragment D-dimer specific humanized monoclonal antibody and a truncated single-chain urokinase

A recombinant chimeric plasminogen activator consisting of a humanized monoclonal antibody specific for cross-linked human fibrin (MA-15C5Hu) and a 32 kDa single-chain urokinase-type plasminogen activator (scu-PA-32k) comprising amino acids Leu144-Leu411, MA-15C5Hu/scu-PA-32k, was previously found to have a 12-fold higher fibrinolytic potency than recombinant scu-PA-32k towards a human plasma clot in a human plasma milieu in vitro (Vandamme et al., Eur J Biochem 1992; 205: 139-46). Therefore, the thrombolytic and pharmacokinetic properties of MA-15C5Hu/scu-PA-32k were compared with those of recombinant single-chain urokinase-type plasminogen activator (scu-PA) in 3 different venous thrombosis models in vivo. In hamsters with a pulmonary embolus consisting of a human plasma clot, the thrombolytic potency (% lysis per dose in mg/kg administered) of MA-15C5Hu/scu-PA-32k was 23-fold higher than that of scu-PA (p less than 0.0005). In rabbits with a jugular vein clot prepared from human plasma, the thrombolytic potency of MA-15C5Hu/scu-PA-32k was 11-fold higher than that of scu-PA (p = 0.012). In baboons with an autologous whole blood clot in the femoral vein, the chimera had a 5-fold higher thrombolytic potency than scu-PA. In all three animal species, the clearance of the chimera was 10- to 27-fold reduced as compared to scu-PA. The specific thrombolytic activity (% lysis per micrograms/ml steady-state plasma u-PA antigen) was increased up to 7-fold with MA-15C5Hu/scu-PA-32k as compared with scu-PA, which is indicative of targeting of the chimera to the clot. No fibrinogen breakdown or alpha 2-antiplasmin depletion was observed during thrombolysis with the chimera. Thus, MA-15C5Hu/scu-PA-32k constitutes a recombinant chimeric plasminogen activator with a significantly enhanced thrombolytic potency in 3 different animal models of venous thrombosis.     

Mineralocorticoids and hypertension]

The degree of lumen narrowing in advanced lesions correlates poorly with the amount of intimal mass accumulated in the atherosclerotic plaque. As an alternate mechanism of stenosis, we propose that human smooth muscle cells bind to fibrin deposited in the matrix and exert contractile forces to cause a narrowing of the lumen. In the present study we demonstrated in vitro that human newborn aortic smooth muscle cell lines can contract and adhere to fibrin clots composed of either fibronectin-depleted plasma ("plasma") or recombinant fibrin. By using neutralizing antibodies and RGD peptides, we showed that members of the integrin family mediated the interaction between human newborn smooth muscle cells and fibrin. Neutralizing antibodies against the integrin alphavbeta3 (c7E3 Fab and LM609) did not inhibit either plasma clot contraction or recombinant fibrin clot contraction by human newborn smooth muscle cells. In contrast, antibodies against alpha5, beta1, and alpha5/beta1 inhibited contraction of clots composed of either plasma or recombinant fibrin. Anti-alphavbeta3, anti-alphav, anti-alpha5, anti-beta1, and anti-alpha5beta1 antibodies inhibited human newborn smooth muscle cell adhesion to plasma clots; however, only anti-alpha5, anti-beta1, and anti-alpha5beta1 antibodies significantly inhibited adhesion to recombinant fibrin. While the linear RGD peptides had no effect, the cyclic peptide penRGD inhibited adhesion to plasma clots and recombinant fibrin. However, it did not block contraction of recombinant fibrin clots. These results suggest that during the interaction of human newborn smooth muscle cell lines with fibrin, alpha5beta1 plays a significant role. This interaction is of potential interest as a target for efforts to block vascular contraction.     

Plasminogen activator inhibitor-1 secretion of endothelial cells increases fibrinolytic resistance of an in vitro fibrin clot: evidence for a key role of endothelial cells in thrombolytic resistance

Time-dependent thrombolytic resistance is a critical problem in thrombolytic therapy for acute myocardial infarction. Platelets have been regarded as the main source of plasminogen activator inhibitor-1 (PAI-1) found in occlusive platelet-rich clots. However, endothelial cells are also known to influence the fibrinolytic capacity of blood vessels, but their ability to actively mediate time-dependent thrombolytic resistance has not been fully established. We will show that, in vitro, tumor necrosis factor-alpha-stimulated endothelial cells secrete large amounts of PAI-1 over a period of hours, which then binds to fibrin and protects the clot from tissue plasminogen activator-induced fibrinolysis. In vivo, endothelial cells covering atherosclerotic plaques are influenced by cytokines synthesized by plaque cells. Therefore, we propose that continuous activation of endothelial cells in atherosclerotic blood vessels, followed by elevated PAI-1 secretion and storage of active PAI-1 in the fibrin matrix, leads to clot stabilization. This scenario makes endothelial cells a major factor in time-dependent thrombolytic resistance.     

Intraventricular and brachial artery thrombosis in nephrotic syndrome

PURPOSE: To investigate the influence of hyperthermia up to 45 degrees C on fibrinolysis with recombinant tissue-type plasminogen activator (rt-PA). METHODS: Standardized fibrin clots were incubated in a water bath for 5 hr with either rt-PA (test group) or 0.9% sodium chloride (control group) and blood plasma at temperatures of 30-45 degrees C. Concentrations of D-dimer and time to complete clot lysis were measured. RESULTS: The activity of fibrinolysis with rt-PA rose with increasing temperature: time to lysis approximately halved from 30 degrees C to 40 degrees C and the concentration of D-dimer tripled. In the control group clot size did not change. CONCLUSIONS: Activity of rt-PA-induced fibrinolysis rises distinctly with higher temperatures. Since even healthy subjects show a physiologic decline in body temperature in the extremities, in patients with occlusive arterial disease decreased activity of fibrinolysis with rt-PA can be expected. Controlled hyperthermia may improve fibrinolysis with rt-PA and should be investigated in vivo.     

Variations in breast cancer treatment by patient and provider characteristics

PURPOSE: To create a simple and reproducible model of chromic thrombosis for the evaluation of thrombolytic agents and devices. MATERIALS AND METHODS: A stenosis was created in the superficial femoral artery of domestic swine, and autologous blood clot was deposited above the stenosis. Follow-up last for up to 3 months. Degree of clot organization was determined at histologic examination. Two thrombolytic agents, urokinase and collagenase, were used to test this model. RESULTS: There was a 27% delayed recanalization rate with this model. At histologic examination, early thrombus organization was seen at the vessel periphery after 10 days. One-month-old thrombus was substantial but variable in amount. Three-month-old thrombus was completely organized. Neither urokinase nor collagenase proved effective against chronic clot in the doses and time course of this study. CONCLUSION: This simple method yields a chronic porcine clot in a reliable number of domestic swine in 1 month.     

Intraoperative high-dose regional urokinase infusion for cerebrovascular occlusion after carotid endarterectomy

Operative stroke complicating carotid endarterectomy is traditionally treated by reexploration of the operative site to correct a potentially causative lesion; however, attempts are not made to diagnose or treat the intracranial arterial occlusion. A 65-year-old man had a right hemiplegia during a left carotid endarterectomy that was caused by premature reversal of heparin, which resulted in thrombosis of his left anterior cerebral artery. On reexploration, the patient was treated with a 1-hour infusion of 1 million U urokinase through an indwelling carotid shunt. A repeat arteriogram demonstrated patency of the left anterior cerebral artery, with complete clot dissolution and resolution of the right hemiplegia on awakening. Natural history studies of stroke and prospective, angiographically controlled clinical trials of intraarterial thrombolytic therapy for acute stroke support the use of intraoperative intraarterial infusion of urokinase as part of a therapeutic approach to patients who have an ischemic stroke during carotid endarterectomy.     

Molecular basis of fibrinolysis, as relevant for thrombolytic therapy

The fibrinolytic system comprises an inactive proenzyme, plasminogen, that is converted by plasminogen activators to the active enzyme, plasmin, that degrades fibrin. Two physiological plasminogen activators have been identified: tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). Plasminogen activation for clot lysis is regulated by specific molecular interactions between tissue-type plasminogen activator (t-PA), plasminogen and fibrin, whereby the lysine-binding sites of the plasminogen molecule play a crucial role by mediating its binding to fibrin, and by controlling the inhibition rate of plasmin by alpha 2-antiplasmin. The recognition that thrombosis within the infarct related coronary artery plays a major role in the pathogenesis of acute myocardial infarction and the observation that early administration of thrombolytic agents results in recanalization of occluded coronary arteries, have provided the basis for the development of thrombolytic therapy in acute myocardial infarction. The elucidation of the biochemical mechanism of fibrin-specific plasminogen activation has fueled the hope that specific and efficacious thrombolytic agents might become available. Comparative studies between the non-fibrin-selective streptokinase and fibrin-selective recombinant t-PA (rt-PA) have shown a difference in efficacy for early coronary artery recanalization, whereas the GUSTO trial has established that clinical benefit in patients with acute myocardial infarction is indeed correlated with the rapidity and frequency of sustained recanalization and that effective thrombolysis requires adequate anticoagulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Rheology of fibrin clots. III. Shear creep and creep recovery of fine ligated and coarse unligated closts

Creep and creep recovery of human fibrin clots in small shearing deformations have been investigated over a time scale from 24 to 10(4) s. Coarse, unligated clots and fine clots ligated by fibrinoligase in the presence of calcium ions were studied to suppliement previous data on coarse ligated and fine unligated clots. Stress was found to be proportional to strain up to at least a maximum shear strain (in torsion geometry) of 6.2%. The initial modulus (25 s after imposition of stress) is proportional to approximately the 1.5 power of concentration for fine ligated and coarse unligated clots. For fine unligated closts there is comparatively little creep subsequent to the initial deformation; ligation (in this case involving mostly the gamma chains) reduces the creep to nearly zero. For coarse unligated clots, there is substantially more creep under constant stress, and creep recovery is not complete. Ligation (in this case involving both camma and alpha chains) alrgely supresses the creep and causes the recovery to be complete. If the structure if fully formed before creep begins, tests of creep recovery by the Boltzmann superposition principle show adherence to linear visoelastic behavior for all four clot types. Otherwise, the Boltzmann test fails and the recovery is much less than calculated. For fine ligated clots, the observed recovery agrees well with that calculated on the basis of a dual structure model in which an additional independent structure is built up in the deformed state, so that the state of ease after removal of stress is a balance between two structures deformed in opposite senses. It is postulated that the coherence and elastic modulus of the fine ligated clot are largely due to steric blocking of long protofibrils with a high flexural stiffness. In the coarse clot, it is proposed that the structure involves extensive branching of thick bundles of protofibrils, which become permanently secured by the ligation of the alpha chains of the fibrin.     

Thrombolytic therapy in acute occlusion of the intracranial internal carotid artery bifurcation

PURPOSE: To evaluate efficacy and clinical benefit of early thrombolytic therapy in intracranial internal carotid artery occlusion. METHODS: Thirty-two patients (mean age, 56 years) with acute intracranial internal carotid artery occlusion were studied clinically and with CT and angiography before and after thrombolytic therapy with intravenous alteplase (n = 16), superselective intraarterial alteplase (n = 8), and superselective intraarterial urokinase (n = 8). RESULTS: Initial CT showed a large parenchymal hypodensity in 11 (34%) patients, a small hypodensity in 15 (47%) patients, and no hypodensity in 6 (19%) patients. Recanalization after thrombolytic therapy was observed in 4 patients (12.5% in each treatment group). Follow-up CT showed six hemorrhagic infarcts and four parenchymal hematomas unrelated to recanalization, alteplase, or urokinase administration, but commonly associated with intraarterial treatment. Clinical outcome was fatal in 53%, poor in 31%, and moderate or good in 16% of the patients. Outcome was equal in different treatment groups and closely linked to both the quality of leptomeningeal collaterals and the extent of parenchymal hypodensity on the first CT. CONCLUSION: Because intravenous or intraarterial treatment with alteplase or urokinase fails to recanalize the vascular obstruction, it does not improve the prognosis of intracranial internal carotid artery occlusion over that of the natural course. Improved results may be possible with novel recanalization techniques.     

A study of the mechanism of inhibition of fibrinolysis by activated thrombin-activable fibrinolysis inhibitor

TAFI (thrombin-activable fibrinolysis inhibitor) is a recently described plasma zymogen that, when exposed to the thrombin-thrombomodulin complex, is converted by proteolysis at Arg92 to a basic carboxypeptidase that inhibits fibrinolysis (TAFIa). The studies described here were undertaken to elucidate the molecular basis for the inhibition of fibrinolysis. When TAFIa is included in a clot undergoing fibrinolysis induced by tissue plasminogen activator and plasminogen, the time to achieve lysis is prolonged, and free arginine and lysine are released over time. In addition, TAFIa prevents a 2.5-fold increase in the rate constant for plasminogen activation which occurs when fibrin is modified by plasmin in the early course of fibrin degradation. The effect is specific for the Glu- form of plasminogen. TAFIa prevents or at least attenuates positive feedback expressed through Lys-plasminogen formation during the process of fibrinolysis initiated by tissue plasminogen activator and plasminogen. TAFIa also inhibits plasmin activity in a clot and prolongs fibrinolysis initiated with plasmin. We conclude that TAFIa suppresses fibrinolysis by removing COOH-terminal lysine and arginine residues from fibrin, thereby reducing its cofactor functions in both plasminogen activation and the positive feedback conversion of Glu-plasminogen to Lys-plasminogen. At relatively elevated concentrations, it also directly inhibits plasmin.     

Dissolution of thrombotic arterial occlusion by high intensity, low frequency ultrasound and dodecafluoropentane emulsion: an in vitro and in vivo study

OBJECTIVES: We examined the effectiveness of the microbubbles of an echo contrast agent, dodecafluoropentane (DDFP) emulsion, to enhance low frequency ultrasound clot disruption in vitro and in vivo. BACKGROUND: Ultrasound is reported to facilitate clot dissolution, and microbubbles could theoretically enhance ultrasound clot dissolution by augmenting cavitational effects. METHODS: In vitro studies: The disruption rate of fresh human clots by ultrasound (24 kHz, 2.9 W/cm2) was examined in saline and DDFP emulsion. In vivo studies: Using a rabbit iliofemoral thrombotic occlusion model, recanalization rate and histopathologic findings were compared among groups treated with DDFP emulsion alone, transcutaneous ultrasound (20 kHz, 1.5 W/cm2) alone and with DDFP emulsion and ultrasound combined. RESULTS: The ultrasound clot disruption rate was significantly (p < 0.01) increased, from 72 +/- 18% (mean +/- SD) in saline to 98 +/- 4% in DDFP emulsion in 3 min in vitro. No vessel was recanalized by DDFP emulsion alone (0%), and only a single artery was patent after ultrasound treatment alone (9%). In contrast, 82% of iliofemoral arteries were angiographically recanalized after ultrasound treatment with DDFP emulsion. Histologically, the patent arteries had only minimal focal mural thrombus, with no evidence of vessel wall damage. However, substantial damage was observed in rabbit dermis and subcutaneous tissue. CONCLUSIONS: 1) DDFP emulsion, an echo contrast agent, significantly enhances the clot-disrupting effect of low frequency ultrasound in vitro and in an in vivo rabbit iliofemoral occlusion model. 2) This simple combination therapy has potential for clinical application in patients with thrombotic arterial occlusions.     

Thrombolysis and endovascular stent placement for inferior vena caval thrombosis in a liver transplant recipient

BACKGROUND: Vascular complications remain an important cause of postoperative morbidity in liver transplant patients. Herein, we present an unusual case of nonanastomotic inferior vena cava (IVC) stenosis in a patient with a "piggyback" caval anastomosis. METHODS: A 59-year-old woman underwent liver transplantation using a piggyback IVC anastomosis. Her postoperative course was complicated by IVC thrombosis. Catheter-directed thrombolysis, followed by balloon angioplasty and intravascular stent placement, was used to recanalize the IVC and treat a severe retrohepatic IVC stenosis. RESULTS: After 46 hr of catheter-directed urokinase infusion, there was clot lysis and identification of a severe stenosis in the retrohepatic IVC. The lesion was extremely resistant to balloon dilatation alone and a 22-mm-diameter intravascular stent was placed. Simultaneous dilatation of three high-pressure balloons was necessary for maximal stent expansion. The patient remains asymptomatic with no evidence of IVC compromise through 20 months of follow-up. CONCLUSIONS: IVC stenosis and thrombosis after liver transplantation may be treated favorably in some patients using catheter-directed thrombolytic therapy followed by balloon dilatation and/or stent placement.     

Plasma TAFI levels influence the clot lysis time in healthy individuals in the presence of an intact intrinsic pathway of coagulation

Thrombin Activatable Fibrinolysis Inhibitor (TAFI) is a recently identified fibrinolysis inhibitor in plasma, that when converted to an enzyme potently attenuates fibrinolysis. It is activated by relatively high concentrations of thrombin that exceed the thrombin concentration required for fibrin formation. These high concentrations of thrombin are generated by the intrinsic pathway via activation of factor XI by thrombin. The down regulation of fibrinolysis by TAFI can be measured in a clot lysis assay. When the clot lysis times of healthy individuals were determined, large inter-individual differences were observed. To determine if differences in concentration of TAFI explain the variation in clot lysis between individuals, specific assays were developed for the measurement of TAFI antigen and activity in plasma. In normal plasma, there was a dose-dependent relationship between TAFI antigen and TAFI activity. There was also a correlation between clot lysis time and plasma TAFI antigen, indicating that the amount of TAFI that is activated during the clot lysis assay, is dependent on the concentration of TAFI. In the plasmas of 20 healthy individuals, clot lysis times, TAFI antigen and TAFI activity were determined. Both TAFI antigen and TAFI activity showed a significant correlation with the clot lysis time. No correlation between TAFI antigen and clot lysis time was found when the clot lysis time was determined in the presence of an antibody blocking the factor XI feedback loop. These results indicate that plasma TAFI levels influence the clot lysis time in healthy individuals in the presence of an intact intrinsic pathway of coagulation.     

Procoagulant nature of fibrin

The main threat from a beginning thrombus is that it tends to grow, and hence become occlusive and/or embolise. Although the progressive nature of thrombi has been recognised since a long time, the mechanisms behind thrombus growth remain only partially resolved. In order to investigate in what ways thrombi can themselves become foci of further thrombin -and hence fibrin-formation, we studied the effect of fibrin clots on thrombin generation in platelet poor--and platelet rich plasma (PPP and PRP). The thrombin always adsorbed on a natural fibrin clot is not inactivated by plasmatic antithrombins and could be shown to retain its ability to enhance further thrombin formation by activation of clotting factors V and VIII as well as of blood platelets. To our surprise, fibrin clots without any active thrombin adsorbed, because they were obtained by a snake-venom enzyme or because thrombin had been inhibited, retained their capacity to activate blood platelets and make them procoagulant. The activation could be shown to be due to a rearrangement of cell-membrane phospholipids, by which the procoagulant species (phosphatidyl serine and phosphatidyl ethanolamine) became available at the outer cell surface. The platelet membrane receptor involved could be recognised as glycoprotein Ib, interacting with fibrin through the plasma protein von Willebrand factor (vWf). In fact it appeared that vWf is indispensable for the generation of thrombin in PRP, with or without added clot. This assigns a new and hitherto unknown role to vWf. Our results also show that fibrin is far from being the inert end-product of coagulation but is a potent activator of blood platelets and by this action may foster thrombin generation and hence further fibrin production. We surmise this mechanism to be instrumental in the progression of thrombotic processes.     

Experimental model of transient cerebral circulatory disorders by way of embolization of cerebral arteries with fresh blood clots

A total of 85 experimental animals received through the blood flux of the carotid arteries clots of autogenic blood of 1 hour age. A histomorphological study after 40 minutes following an embolism there were revealed clots in the cerebral arteries in 13 out of 14 animals. After 1.5 hours in 1 of 17, and after 24 hours in none of the 10 animals. Directly following the administration of clots in all the 20 animals of this series, there were symptoms of focal brain lesions: hemipareses, ptosis and myosis, a "trot around circles", etc. In all 20 animals there was a complete regress of the symptom at different times (from 10 min to 18 hours). In all cases there was an increased amount of lactic acid in the cerebral blood outflow while subsequently was reduced, correlating with the time of clot lysis. The morphological control did not depict brain infarctions. It is assumed that the reason of brain dysfunctions is an obturation by blood clots of cerebral arteries, while their normalization is due to a spontaneous lysis of the embols which obturated the cerebral arteries.     

Urokinase in the management of vitreous hemorrhage

Urokinase is a plasminogen activator of human origin which breaks up the fibrin base of blood clots. When given as an intravitreal injection it produces hypopyon and glaucoma, both of which transient. In a series of 27 patients (34 eyes) with unresolved vitreous haemorrhage, this simple and relatively atraumatic treatment has produced marked objective improvement in 10, and greatly improved the life styles of a further 9. This series brings the total of reported cases to 93. When compared with recent American reports of surgical vitrectomy for vitreous haemorrhage, intravitreal urokinase appears to have a higher success rate, with a lower complication rate both in the short and long term. This study suggests that, despite the high cost of the purified enzyme, urokinase should be come the first line of attack in vitreous haemorrhage, vitrectomy being reserved for those patients who fail to respond.