Efficiency Of Thrombolysis Research Articles

Thrombolysis efficiency of urokinase plasminogen activator-loaded anionic lipid microbubbles combined with low-frequency ultrasound in vitro

Objective To prepare urokinase plasminogen activator (uPA)-loaded anionic lipid microbubbles (uPA-MBs) for thrombolysis with low-frequency ultrasound in vitro.Methods Anionic microbubbles composing of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC),1,2-dipalmitoyl-sn-glycero-3-phospho-(l'-rac-glycerol) (DPPG),1,2-distearoyl-sn-glycero-3-phosphoethanol amine-N (succinyl PEG2000) (DSPE-PEG2000) and perfluoropropane (C3F8) were prepared by the mechanical vibration method.Then,the resulting anionic microbubbles were incubated with uPA.uPA-MBs were obtained via electrostatic adsorption.Bubble size and distribution were measured by particle size analyzer.FITC-labeled uPA-MBs were obtained and observed under fluorescence microscope.The surface potential of uPA-MBs and plain microbubbles (P-MBs) were detected by Zeta potential analyzer.Sodium dodecyl sulfonate-polyacrylamide gel electrophoresis (SDS-PAGE) was used for confirming the binding of uPA protein and anionic microbubbles.The encapsulation efficiency of uPA-MBs was determined by bicinchoninic acid (BCA) protein assay kit under three different dosages of uPA (10 000,50 000 and 100 000 U).The thrombolysis efficiency of uPA-MBs combined with low-frequency ultrasound was examined in vitro.Two-sample t test,one-way analysis of variance and Bonferroni test were performed to analyze the data.Results UPA-MBs were successfully obtained with the mean particle size of (1.76±0.29) μm.The surface potential of these bubbles was significantly higher than that of P-MBs:(-36.64±0.21) mV vs (-66.33±2.38) mV (t =21.538,P＜0.05).Fluorescence microscope showed a green shell of FITC-labeled uPA-MBs.The encapsulation efficiency of uPAMBs with the added dosage of 10 000 U was (42.01±2.02) ％,which was significantly higher than those of 50000 and 100 000 U ((33.24±1.95)％ and (33.10±1.65)％ respectively,F=22.340,P＜0.05).The thrombolysis efficiency by saline was (4.09±0.80)％,saline + ultrasound (8.50±1.48)％,MBs + ultrasound (14.27± 1.59) ％,uPA-MBs + ultrasound (35.72±6.31) ％ and uPA (16.87±0.46) ％,respectively (F =48.783,t =-8.613,-7.273,-5.942,-6.908,all P＜0.05).Conclusion Anionic microbubbles can successfully load uPA,and achieve significantly better thrombolysis effect when combined with low-frequency ultrasound. Key words: Thrombolytic therapy ; Microbubbles ; Urokinase ; Ultrasonography

Effect Of Education To Hospital Staff On Efficiency Of Acute Stroke Thrombolysis (P3.105)

Effect Of Education To Hospital Staff On Efficiency Of Acute Stroke Thrombolysis (P3.105)

Construction and Evaluation of Fe3O4-Based PLGA Nanoparticles Carrying rtPA Used in the Detection of Thrombosis and in Targeted Thrombolysis

Thrombotic disease is extremely harmful to human health, but early detection and treatment can help improve prognoses and reduce mortality. To date, few studies have used MR molecular imaging in the early detection of thrombi and in the dynamic monitoring of the thrombolytic efficiency. In this article, we construct Fe3O4-based poly(lactic-co-glycolic acid) (PLGA) nanoparticles to use in the detection of thrombi and in targeted thrombolysis using MRI monitoring. Cyclic arginine-glycine-aspartic peptide (cRGD) was grafted onto the chitosan (CS) surface to synthesize a CS-cRGD film using carbodiimide-mediated amide bond formation. A double emulsion solvent evaporation method (water in oil in water [W/O/W]) was used to construct Fe3O4-based PLGA nanoparticles carrying recombinant tissue plasminogen activator (rtPA) (Fe3O4-PLGA-rtPA/CS-cRGD). Fe3O4-PLGA, Fe3O4-PLGA-rtPA, and Fe3O4-PLGA-rtPA/CS nanoparticles were constructed using the same W/O/W method. The results showed that the Fe3O4-based nanoparticles were constructed successfully and have a regular shape, a relatively uniform size, a high carrier rate of Fe3O4 and encapsulation efficiency of rtPA, and a relatively high activity of released rtPA. Transmission electron microscope (TEM) images revealed that the iron oxide particles were relatively uniformly distributed in the nano-spherical shell. The Fe3O4-based nanoparticles could be imaged using a clinical MRI scanner, and there were no significant differences in the transverse relaxation rate (R2*) or in the signal-to-noise ratio (SNR) values between the Fe3O4-based nanoparticles and an Fe3O4 solution with the same concentration of Fe3O4. In vitro and in vivo experiments confirmed that the Fe3O4-PLGA-rtPA/CS-cRGD nanoparticles specifically accumulated on the edge of the thrombus and that they had a significant effect on the thrombolysis compared with the Fe3O4-PLGA, Fe3O4-PLGA-rtPA, and Fe3O4-PLGA-rtPA/CS nanoparticles and with free rtPA solution. These results suggest the potential of the Fe3O4-PLGA-rtPA/CS-cRGD nanoparticles as a dual-function tool in the early detection of a thrombus and in the dynamic monitoring of the thrombolytic efficiency using MRI.

PT137 Evaluation of thrombolysis versus primary percutaneous coronary intervention (PCI) outcomes for patients with early presentation (within 60 minutes) of acute ST elevation myocardial infarction (STEMI)

EF 49 12 45 16 NS P O ST E R A B ST R A C T S percutaneous coronary intervention (PCI), as thrombolysis can be administered within few minutes of STEMI diagnosis. Metropolitan hospitals are equipped with more staff, access to physician/cardiology and sufficient resources for further treatment compared to rural centres. It is unclear how these expertise and choices may impact on either expediting or delaying decision making in revascularization strategies. Objectives: Compare efficiency of thrombolysis in rural versus greater Brisbane metropolitan areas in those patients with acute STEMI. Methods: Acute STEMI patients who were directly or eventually referred to a tertiary centre in Brisbane (Princess Alexandra Hospital) over a 4 months period were identified. The onset to needle time (OTN), first diagnostic ECG to needle times and Door to needle (DTN) times were estimated in patients presenting with acute STEMI within 6 hours. Maximum creatine kinase (CK) rise used as the assessment of the extent of myocardial infarction. Results: A total of 195 (average age 61yrs, 78% male) acute STEMI patients were prospectively reviewed over the past 4 months. The Table 1 and 2 below shows the results in detail.

The ischemic penumbra

The clinical efficiency of thrombolysis is explained by the rescue of ischemic penumbra areas resulting from early arterial recanalization. The perfusion-diffusion weighted imaging mismatch is a commonly used MRI surrogate of the ischemic penumbra. However, the randomized trials testing the mismatch hypothesis have been negative. We will review the 'mismatch concept' and the recent studies that aim to localize the clinically eloquent areas of penumbra in middle cerebral artery (MCA) infarcts. New methods of image analysis have shown that poor outcomes after MCA stroke are related to infarction of an extremely well localized area of the periventricular white matter and adjacent internal capsule, where projections and association tracts are crossing and converging. This area almost colocalizes with the area salvaged by early arterial recanalization and is located extremely close to the initial ischemic core. The location of the area that correlates with disability in MCA stroke patients and that is salvaged by early arterial recanalization is in the same specific region of the deep white matter, close to the initial ischemic core. These findings may have important implications for designing new recanalization trials and support the importance of basic research on white-matter neuroprotection.

In vitro demonstration of focused ultrasound thrombolysis using bifrequency excitation.

Focused ultrasound involving inertial cavitation has been shown to be an efficient method to induce thrombolysis without any pharmacological agent. However, further investigation of the mechanisms involved and further optimization of the process are still required. The present work aims at studying the relevance of a bifrequency excitation compared to a classical monofrequency excitation to achieve thrombolysis without any pharmacological agent. In vitro human blood clots were placed at the focus of a piezoelectric transducer. Efficiency of the thrombolysis was assessed by weighing each clot before and after sonication. The efficiencies of mono- (550 kHz) and bifrequency (535 and 565 kHz) excitations were compared for peak power ranging from 70 W to 220 W. The thrombolysis efficiency appears to be correlated to the inertial cavitation activity quantified by passive acoustic listening. In the conditions of the experiment, the power needed to achieve 80% of thrombolysis with a monofrequency excitation is reduced by the half with a bifrequency excitation. The thermal effects of bifrequency and monofrequency excitations, studied using MR thermometry measurements in turkey muscle samples where no cavitation occurred, did not show any difference between both types of excitations when using the same power level.

Role of thrombolytic therapy in young adult smokers with acute ST-elevation myocardial infarction

IntroductionSTEMI is a major cause of cardiovascular mortality worldwide. Smoking seems to be the most common risk factor seen in both young and the old population. Atherosclerotic plaques are more commonly seen in older population. In young smoking adults the clots are not atherosclerotic. As smoking causes endothelial injury along with “sticky phenomenon”, where the fibrin sticks together in presence of thrombin and forms clots. The thrombolytic efficiency lays in its specificity to fibrin. This makes thrombolytic drugs the preferential treatment in young adults due to their clots (fibrin and thrombin) than older patient's atherosclerotic plaques (cholesterol, fibrin and thrombin). MethodOnly patients diagnosed with acute STEMI and treated with Thrombolytic therapy were included in this study. ResultsOur study showed that TLT was effective in recanalising the infarct related artery in the young adult smokers when compared to the old adults with acute STEMI. Age is a statistically significant variable (p < 0.0001), where the percentage of recanalised patients increases with decreasing age (i.e., young patients recanalise more than the older patients). Also the effect of smoking on recanalisation of the culprit coronary artery is statistically significant (p = 0.056). And when we look at the group of young adults, the effect of smoking on number of recanalisations has an odds ratio of 2.57, which can be interpreted as, smokers are 2.57 times are likely to recanalise the infarct related artery when compared to non-smokers. ConclusionAlthough Percutaneous Coronary Intervention (PCI) has been proven beneficial over TLT in management of acute STEMI, thrombolytics are recanalising the younger patients better than the older patients. TLT has a special place in young smokers as it targets the fibrin breakdown and therefore accounts for higher recanalisation rates, as most of their clots are due to thrombus formation made of fibrin and thrombin.

Abstract TP254: Clot Dissolution Is Better With Ultrasound Assisted Thrombolysis For Fresh Clots With Higher Cholesterol Content

Background: Intravenous tissue plasminogen activator (IV-tPA) remains the only drug for arterial recanalization in acute ischemic stroke (AIS). Clot composition differs according to the stroke etiology- clot from heart being fresh and rich in fibrin while the clot from an ulcerated plaque is rich in cholesterol. These characteristics might influence the therapeutic response to tPA as well as ultrasound-enhanced thrombolysis. We evaluated the impact of cholesterol content and age of the clot on its dissolution with tPA and ultrasound in an in-vitro model. Methods: Clot was prepared by mixing horse blood with Calcium-chloride solution. Cholesterin was added to increase cholesterol level up to 100 mg/dL. Periodic serum replacement was used to ‘age’ the clot. The clots were exposed to continuous 2-MHZ diagnostic transcranial Doppler (TCD) ultrasound (acoustic intensity 340mW/cm2) during thromolysis with tPA (355 IU/ml). Efficiency of thrombolysis was calculated as the percentage of clot weight-loss after 60 minutes. Clot characteristics after lysis were evaluated with surface emission microscope (SEM). Results: Significant increase in the weight of clot occurred with its increasing age (from 2 to 10 hours, the clot-weight increased from 37.28±2.87mg to 51.56±5.34mg; p&lt;0.005). Exposure to ultrasound and tPA resulted in significant reduction in the clot-weight at 1 hour (from 35.50±3.23% to 24.71±2.11%; p&lt;0.005). Although, no significant differences were noted between clot-cholesterol levels and lysis with TCD or tPA alone, combination of these modalities induced significant lysis in clots with higher cholesterol levels (clot-weight reduced by 41.68±2.3%) as compared to clots with normal cholesterol (30.60±4.10%; p&lt;0.005). SEM demonstrated thicker and denser fibrin network in aged clots while higher number of activated platelets were noted on the surface of cholesterol-rich clots. Conclusion: Ultrasound-assisted thrombolysis with tPA work better for fresh thrombi with higher cholesterol levels. Our findings provide insights into the differential recanalization rates in acute ischemic stroke of various etiologies

Laser enhanced high-intensity focused ultrasound thrombolysis: An in vitro study

Laser-enhanced thrombolysis by high intensity focused ultrasound (HIFU) treatment was studied in vitro with bovine blood clots. To achieve laser-enhanced thrombolysis, laser light was employed to illuminate the sample concurrently with HIFU radiation, and ultrasound and laser parameters were optimized to achieve better thrombolysis efficiency. The results indicated that the thrombolysis efficiency increased when pulse length of HIFU wave, HIFU pressure, or laser fluence increases. Also, with the presence of laser, an enhanced effect of thrombolysis was observed.

Transcatheter thrombolytic therapy for symptomatic thrombo-occlusion of inferior vena cava filter

Thrombus within an inferior vena cava (IVC) filter reduces filter patency and venous return from the lower extremities, and may progress to complete IVC occlusion. The clinical experiences and outcomes of transcatheter thrombolytic therapy for symptomatic IVC thrombosis following filter implantation have not been widely reported. The aim of the current study was to evaluate the efficiency and safety of trans-catheter thrombolysis for the treatment of symptomatic IVC thrombosis in patients with implanted IVC filters. Transcatheter thrombolysis was used to treat 5 patients with thrombosis of the filter-bearing IVC causing symptoms in 10 limbs from October 2005 to September 2010. The patients were implanted with a second IVC filter through the right internal jugular vein, followed by recanalization of the occluded IVC and intravenous transcatheter thrombolysis. The IVC filters were retrieved through the femoral or right internal jugular vein after the thrombus had dissolved. Technical and clinical outcome, complications and postoperative pulmonary embolism were monitored. A total of 5 filters were implanted and 6 filters were retrieved later. Technically and clinically successful recanalization and thrombolysis were achieved in 5 of 5 patients and 10 of 10 symptomatic limbs. The median thrombolysis period was 13 days (range, 8–14 days). The median dwell time for the filters that were removed was 50.5 days (range, 14–73 days). No major bleeding occurred during the current study. During clinical follow-up, no clinically detectable pulmonary embolism was observed. Endovascular recanalization and transcatheter thrombolysis of IVC thrombosis are efficient, feasible and safe in the presence of an IVC filter.

Modulation by the noble gas argon of the catalytic and thrombolytic efficiency of tissue plasminogen activator

Argon has been shown to provide cortical as well as, under certain conditions, subcortical neuroprotection in all models so far (middle cerebral artery occlusion, trauma, neonatal asphyxia, etc.). This has led to the suggestion that argon could be a cost-efficient alternative to xenon, a metabolically inert gas thought to be gold standard in gas pharmacology but whose clinical development suffers its little availability and excessive cost of production. However, whether argon interacts with the thrombolytic agent tissue plasminogen activator, which is the only approved therapy of acute ischemic stroke to date, still remains unknown. This latter point is not trivial since previous data have clearly demonstrated the inhibiting effect of xenon on tPA enzymatic and thrombolytic efficiency and the critical importance of the time at which xenon is administered, during or after ischemia, in order not to block thrombolysis and to obtain neuroprotection. Here, we investigated the effect of argon on tPA enzymatic and thrombolytic efficiency using in vitro methods shown to provide reliable prediction of the in vivo effects of both oxygen and the noble inert gases on tPA-induced thrombolysis. We found that argon has a concentration-dependent dual effect on tPA enzymatic and thrombolytic efficiency. Low and high concentrations of argon of 25 and 75vol% respectively block and increase tPA enzymatic and thrombolytic efficiency. The possible use of argon at low and high concentrations in the treatment of acute ischemic stroke if given during ischemia or after tPA-induced reperfusion is discussed as regards to its neuroprotectant action and its inhibiting and facilitating effects on tPA-induced thrombolysis. The mechanisms of argon-tPA interactions are also discussed.

Development of Endovascular Vibrating Polymer Actuator Probe for Mechanical Thrombolysis

In this study, we propose a new method for the enhancement of intraarterial thrombolysis by use of an endovascular vibrating polymer actuator probe (VPAP), which is fabricated from an ionic polymer metal composite (IPMC) actuator. The endovascular VPAP was fabricated by combining 0.8 × 0.8 × 10 mm3 IPMC samples, 0.22 mm × 50 cm copper wires, and 40 cm of Teflon tube. The purpose of this study was to evaluate the thrombolysis efficiency of an endovascular VPAP in a dog model. Both renal arteries of the enrolled dogs (n = 5) were used in the current study. A distal portion of the renal artery in a mongrel dog was occluded by a blood clot from autologous venous whole blood. Intraarterial thrombolysis was performed by use of a VPAP without the actuation force (control group), by a VPAP-only (VPAP-only group), or with a combination of recombinant tissue plasminogen activator (rtPA) and a VPAP (VPAP + rtPA group). The thrombolysis efficiency was evaluated by the modified Thrombolysis in Myocardial Infarction (TIMI) grading system based on the consensus between two radiologists. The grading scales were compared according to each intraarterial thrombolysis method. The VPAP + rtPA and VPAP-only groups showed a significantly higher thrombolysis efficiency than did the control group (p < 0.05). The VPAP-only group also showed a significantly higher thrombolysis efficiency than did the control group (p < 0.05). The VPAP+ rtPA group showed a significantly higher thrombolysis efficiency than did the VPAP-only group (p < 0.05). The use of an endovascular VPAP was a feasible and useful method for intraarterial thrombolysis, and it enhanced the thrombolysis efficiency when combined with the thrombolytic agent rtPA.

How Do Microbubbles and Ultrasound Interact? Basic Physical, Dynamic and Engineering Principles

Ultrasound contrast agents consisting of gas microbubbles stabilised by a polymer or surfactant coating have been in clinical use for several decades. Research into the biomedical uses of microbubbles, however, remains a highly active and growing field. This is largely due to their considerable versatility and the wide range of applications for which they have demonstrated potential benefits. In addition to contrast enhancement, diagnostic applications include: perfusion mapping and quantification and molecular imaging. In drug and gene therapy microbubbles can be used as vehicles which are inherently traceable in vivo and can provide both targeted and controlled release. In addition, the dynamic behaviour of the microbubbles in response to ultrasound excitation contributes to the therapeutic process. At low intensities microbubbles have been shown to mediate reversible enhancement of cell and endothelial permeability, including temporary opening of the blood brain barrier. At higher intensities they have been used as means of increasing the efficiency of thrombolysis, high-intensity focused ultrasound (HIFU) surgery and lithotripsy. The aim of this review is to describe the key physical principles which determine how microbubbles and ultrasound interact and the implications for their design, preparation and exploitation in diagnostic and therapeutic applications.

Abstract 2399: Protocol for Rapid Acquisition and Interpretation of Head CT in Acute Stroke Patients Eligible for Thrombolysis

Introduction The American Heart Association’s quality improvement initiative, Target Stroke, is designed to reduce door-to-needle (DTN) times for IV r-tPA to improve patient outcomes. One of the quality indicators is time-to-CT scan and interpretation. Although, we were already meeting the recommended target, we sought to further enhance efficiency of this process in our institution. Method We performed a retrospective chart review of patients with CT Brain Acute Stroke protocol orders from January to December 2010, which represents a one-year period after instituting changes to our CT protocol. Some of the changes included: improved emergency medical service communication, streamlined patient registration and emergency department (ED) training on time-sensitive stroke care elements. CT scan times were analyzed based on time ordered, time of completion, and radiology interpretation. Our review included DTN for IV r-tPA administration for acute stroke patients during the same time period. Results Of the 571 acute stroke patients admitted through the ED during the study period, 12% received IV r-tPA. Of these, 79% received IV r-tPA within 60 minutes, with a mean (±SD) DTN time of 52 (±27) minutes. The relative efficiency of thrombolysis was attributed in part due to our fast-track CT head protocol process. The mean time from CT order to completion was 12 minutes and CT completion to verbal reporting to the ordering physician was 6 minutes. Conclusion Using a multi-disciplinary approach for quality improvement in CT acquisition and interpretation times, we were able to enhance the efficiency of our overall DTN time. We believe that our protocol is easily adaptable in any Neurointensivist led stroke service, and would benefit patients on a national level to allow for more rapid administration of IV r-tPA by reducing delays in the CT head protocol. Developing a strong infrastructure that is hard-wired and part of the institutional culture resulted in decreased CT times along with 79% of stroke patients receiving r-tPA in less than 60 minutes. Are efforts have paid off; our hospital has been designated on the Target Stroke Honor Roll.

Development of Endovascular Vibrating Polymer Actuator Probe for Mechanical Thrombolysis: A Phantom Study

In this study, we propose a new method for enhancement of intraarterial thrombolysis using an ionic polymer-metal composite (IPMC) actuator. The purpose of this study was to test the mechanical thrombolysis efficiency of IPMC actuators and evaluate the endovascular vibrating polymer actuator probe for mechanical thrombolysis in a phantom model; 2 × 1 × 15 mm (2 mm in width, 1 mm in thickness, and 15 mm in length) and 0.8 × 0.8 × 10 mm (0.8 mm in width, 0.8 mm in thickness, and 10 mm in length) IPMC actuators were fabricated by stacking five and four Nafion-117 films, respectively. We manufactured the endovascular vibrating polymer actuator probe, for which thrombolysis efficiency was tested in a vascular phantom. The phantom study using 2 × 1 × 15 mm IPMC actuators showed that 5 Hz actuation is the optimal frequency for thrombolysis under both 2 and 3 V, when blood clot was not treated with rtPA, and when exposed to rtPA, IPMC actuators under the optimized condition (3 V, 5 Hz, and 5 min) significantly increased the thrombolysis degree compared with control and other experimental groups (p < 0.05). In addition, 0.8 × 0.8 × 10 mm IPMC actuators also revealed a significantly higher thrombolysis degree under the optimized condition than the control and rtPA only groups (p < 0.05). Finally, the fabricated probe using 0.8 × 0.8 × 10 mm IPMC actuators also incurred higher thrombolysis degree under the optimized condition than the control and rtPA only groups (p < 0.05). A vibrating polymer actuator probe is a feasible device for intravascular thrombolysis, and further study in an animal model is warranted.

Thrombolysis as a factor associated with favorable outcomes in patients with unclear-onset stroke

Clinical and radiological features of patients with unclear-onset stroke do not differ significantly from those with known-onset stroke. There is a lack of evidence for the safety and efficacy of thrombolysis in patients with unclear-onset stroke. We sought to provide supportive data on the safety and efficiency of thrombolysis in patients with unclear-onset stroke. We retrospectively identified patients with unclear-onset stroke (<3 h of first found abnormal time) from our stroke registry. We performed following protocols for thrombolysis in patients with unclear-onset stroke; initial conventional CT-based intravenous thrombolysis (IVT), repeat MRI during IVT, and then decision to maintain IVT or to perform combined intra-arterial thrombolysis. In addition, we compared clinical outcomes and safety between thrombolyzed and non-thrombolyzed patients. A total of 78 patients with unclear-onset stroke were included. Twenty-nine patients underwent thrombolysis. Thrombolysis (OR, 6.842; 95% CI, 1.950-24.004; P = 0.003) and baseline NIHSS (OR, 0.769; 95% CI, 0.645-0.917; P = 0.003) were associated with favorable outcomes at 3 months in multivariate logistic regression analysis. The frequency of hemorrhagic transformation and symptomatic ICH was not significantly different between the thrombolyzed and non-thrombolyzed patients (34.4% vs. 40.7% and 10.3% vs. 8.2%, respectively). The results of this study suggest that thrombolysis in unclear-onset stroke could be independently associated with favorable outcomes at 3 months and that thrombolysis based on repeat imaging appears to be safely applied to patients with unclear-onset stroke.

Carboxypeptidase U (TAFIa): a new drug target for fibrinolytic therapy?

Procarboxypeptidase U (TAFI) is a recently discovered plasma procarboxypeptidase that upon activation by thrombin or thrombin-thrombomodulin turns into a potent antifibrinolytic enzyme. Its prominent bridging function between coagulation and fibrinolysis raised the interest of many research groups and of the pharmaceutical industry. The development of carboxypeptidase U (CPU) inhibitors as profibrinolytic agents is an attractive concept and possibilities for rational drug design will become more readily available in the near future as a result of the recently published crystal structure. Numerous studies have been performed and many of them show beneficial effects of CPU inhibitors for the improvement of endogenous fibrinolysis in different animal sepsis and thrombosis models. CPU inhibitors combined with tissue-type plasminogen activator (t-PA) seem to increase the efficiency of pharmacological thrombolysis allowing lower dosing of t-PA and subsequently fewer bleeding complications. This review will focus on recently obtained in vivo data and the benefits/risks of targeting CPU for the treatment of thrombotic disorders.

The Role of Thrombolysis in Acute Infrainguinal Bypass Occlusion: A Prospective Nonrandomized Controlled Study

Current treatment of acute infrainguinal bypass occlusion consists of either surgical revascularization or catheter-guided intra-arterial thrombolysis with adjunctive correction of the underlying flow-limiting lesion. In maintaining long-term patency, improving the number of outflow vessels could be of utmost importance. To compare the efficiency of both thrombolysis and primary surgical revascularization and to study the effect of thrombolysis on the number of patent outflow vessels, a prospective nonrandomized study was performed. Between February 2002 and August 2003, 54 patients with 56 occluded bypasses were included. Thirty bypasses were treated with thrombolysis, 26 primarily with surgery. Thrombolysis was successful in 80% of cases, with restoration of patency of the bypass but also with doubling of the amount of patent outflow vessels; surgery was successful in 85.71% of cases. However, in only 60% of the successfully lysed bypasses no adjunctive major surgery was needed. Amputation-free survival was 87.5% 1 year after surgery and 82.6% 1 year after thrombolysis. One year after thrombolysis without adjunctive major surgery, the amputation-free survival was only 39.7%. Therefore, a strategy could be to start with thrombolysis to improve outflow followed by a new bypass, whatever the underlying causative lesions are.

TPA as an ‘interface’ between blood and brain

Over the last decade, tPA has been implicated in a variety of brain functions. It is secreted from growth cones or extending neurites, it modulates neurite outgrowth and promotes neuronal migration. tPA has also been involved in physiological glutamatergic-dependent processes such as synaptic plasticity and long term potentiation. In addition, t-PA has been shown to play an important role in the pathogenesis of seizure, multiple sclerosis, trauma and ischemic brain injury. In a previous study, we have shown that the proteolytic activity of t-PA enhances the N-methyl-D-aspartate (NMDA) receptor-mediated signalling (Nicole et al., 2001). Here, we provide evidences that tPA is able to cross the intact blood brain barrier both in vitro and in vivo and that this mechanism is independent of its proteolytic activity and mediated by an interaction with a LDL-related receptor, LRP. Overall, these data suggest that blood-derived tPA could influence neuronal functioning. Accordingly, intravenous injection of tPA potentiates the NMDA-induced brain lesion in rats even in the absence of blood brain barrier leakage. As a model demonstrating that preventing the NMDA-dependent effect of tPA could improve the efficiency of thrombolysis in the treatment of stroke, we evidence that the blood-derived tPA failed to enhance NMDA-dependent signalling in a model of mice previously vaccinated with the amino-terminal domain (ATD) of NR1 subunit of the NMDA receptor. Thus, we propose a new concept suggesting that tPA is one of the key element of the interface between the blood and the brain parenchyma.

Influence of ultrasound operating parameters on ultrasound-induced thrombolysis in vitro

The effect of operating parameters on the thrombolytic potency of ultrasound (US) is important for potential therapeutic applications, but is not fully understood. Fresh human whole-blood thrombi were exposed in vitro to focused US from a diagnostic transducer driven by an impulse generator via an amplifier to vary duration (10 to 60 min), intensity (7 to 90 W/cm 2), frequency (2 to 4.5 MHz), pulsed wave duty cycle (1:5 to 1:100 and continuous wave mode) and pulse length (100 to 400 μs). Segments of thrombi (498 ± 73 mg) were submersed and insonated in saline solution. Thrombolytic efficiency was expressed as percentage loss of mass compared with controls (noninsonified thrombi). Ultrasound exposure achieved a significantly higher thrombolysis than no US, 56 ± 16 % vs. 29 ± 11 % ( n = 232, p < 10 −6). There was an exponential saturation-type correlation with duration of insonation (r 2 = 0.64) and intensity (r 2 = 0.97), an inverse correlation with US frequency at matched intensities (r 2 = 0.76, p < 10 −5), a logarithmic relationship with duty cycle in pulsed mode (r 2 = 0.86) and a modest direct effect of pulse length (r 2 = 0.57, p < 10 −5). Thus, thrombolytic efficiency of US depends directly on duration, intensity, duty cycle and pulse length and inversely, on frequency. (E-mail: frank.flachskampf@rzmail.uni-erlangen.de)