Distinct dose-dependent effects of plasmin and TPA on coagulation and hemorrhage

Assessment of effectiveness and safety of thrombolytic therapy to pulmonary emboli by endobronchial ultrasound-guided transbronchial needle injection

Objective

Endobronchial ultrasound-guided transbronchial needle injection (EBUS-TBNI) may effectively treat acute pulmonary embolisms (PEs). Here, we assessed the effectiveness of clot dissolution and safety of tissue plasminogen activator (t-PA) injection using EBUS-TBNI in a 1-week survival study of a porcine PE model.

Methods

Six pigs with bilateral PEs were used: 3 for t-PA injection using EBUS-TBNI (TBNI group) and 3 for systemic administration of t-PA (systemic group). Once bilateral PEs were created, each 25 mg of t-PA injection using EBUS-TBNI for bilateral PEs (a total of 50 mg t-PA) and 100 mg of t-PA systemic administration was performed on day 1. Hemodynamic parameters, blood tests, and contrast-enhanced computed tomography scans were carried out at several time points. On day 7, pigs were humanely killed to evaluate the residual clot volume in the pulmonary arteries.

Results

The average of percent change of residual clot volumes was significantly lower in the TBNI group than in the systemic group (%: systemic group 36.6 ± 22.6 vs TBNI group 9.6 ± 6.1, P < .01) on day 3. Considering the elapsed time, the average decrease of clot volume per hour at pre-t-PA to post t-PA was significantly greater in the TBNI group than in the systemic group (mm3/hour: systemic 68.1 ± 68.1 vs TBNI 256.8 ± 148.1, P < .05). No hemorrhage was observed intracranially, intrathoracically, or intraperitoneally on any contrast-enhanced computed tomography images.

Conclusions

This study revealed that t-PA injection using EBUS-TBNI is an effective and safe way to dissolve clots.

Factor VIII: A Dynamic Modulator of Hemostasis and Thrombosis in Trauma

A trace amount of thrombin cleaves factor VIII (FVIII) into an active form (FVIIIa), which catalyzes FIXa-mediated activation of FX on the activated platelet surface. FVIII rapidly binds to von Willebrand factor (VWF) after secretion and becomes highly concentrated via VWF-platelet interaction at a site of endothelial inflammation or injury. Circulating levels of FVIII and VWF are influenced by age, blood type (nontype O > type O), and metabolic syndromes. In the latter, hypercoagulability is associated with chronic inflammation (known as thrombo-inflammation). In acute stress including trauma, releasable pools of FVIII/VWF are secreted from the Weibel-Palade bodies in the endothelium and then augment local platelet accumulation, thrombin generation, and leukocyte recruitment. Early systemic increases of FVIII/VWF (>200% of normal) levels in trauma result in a lower sensitivity of contact-activated clotting time (activated partial thromboplastin time [aPTT] or viscoelastic coagulation test [VCT]). However, in severely injured patients, multiple serine proteases (FXa plasmin and activated protein C [APC]) are locally activated and may be systemically released. Severity of traumatic injury correlates with prolonged aPTT and elevated activation markers of FXa, plasmin, and APC, culminating in a poor prognosis. In a subset of acute trauma patients, cryoprecipitate that contains fibrinogen, FVIII/VWF, and FXIII is theoretically advantageous over purified fibrinogen concentrate to promote stable clot formation, but comparative efficacy data are lacking. In chronic inflammation or subacute phase of trauma, elevated FVIII/VWF contributes to the pathogenesis of venous thrombosis by enhancing not only thrombin generation but also augmenting inflammatory functions. Future developments in coagulation monitoring specific to trauma patients, and targeted to enhancement or inhibition of FVIII/VWF, are likely to help clinicians gain better control of hemostasis and thromboprophylaxis. The main goal of this narrative is to review the physiological functions and regulations of FVIII and implications of FVIII in coagulation monitoring and thromboembolic complications in major trauma patients.

Catheter Directed Thrombolysis for Not Immediately Threatening Acute Limb Ischaemia: Systematic Review and Meta-Analysis

OBJECTIVE

This systematic review and meta-analysis reports the outcomes of catheter directed thrombolysis (CDT) in patients with not immediately threatening (Rutherford I) acute lower limb ischaemia (ALI).

DATA SOURCES

PubMed, Embase, and the Cochrane Library.

REVIEW METHODS

A systematic search of PubMed, Embase, and the Cochrane Library was performed to identify observational studies and trials published between 1990 and 2022 reporting on the results of CDT in patients with Rutherford I ALI. A meta-analysis was performed using a random effects model with 95% confidence intervals (CIs). The outcomes of interests were treatment duration, angiographic success, bleeding complications, amputation and mortality rates, primary and secondary patency, and functional outcome expressed as pain free walking distance.

RESULTS

Thirty-nine studies were included, comprising 1 861 patients who received CDT for not immediately threatening ALI. Funnel plots showed an indication of publication bias, and heterogeneity was substantial. Data from 5 to 13 studies were included in the meta-analysis. The pooled treatment duration was 2 days (95% CI 1 - 2), with an angiographic success rate of 80% (95% CI 73 - 86) and a 30 day freedom of amputation rate of 98% (95% CI 92 - 100). The major bleeding rate was 5% (95% CI 2 - 14), with a 30 day mortality rate of 3% (95% CI 1 - 5). The amputation free survival rate was 71% (95% CI 62 - 80) at the one year and 63% (95% CI 51 - 73) at the three year follow up. Long term patency rates were retrieved from four studies: 48% at one year (95% CI 27 - 70). No data could be retrieved on patient walking distance.

CONCLUSION

Although CDT in the treatment of not immediately threatening ALI showed high angiographic success, the long term outcomes were relatively poor, with low patency and a substantial risk of major amputation. Further research is required to interpret the outcome of CDT in the context of potential confounders such as age and comorbidities.

Major Bleeding During Thrombolytic Therapy for Acute Lower Limb Ischaemia: Value of Laboratory Tests for Clinical Decision Making, 17 Years of Experience

OBJECTIVE

Regular measurement of fibrinogen as dose guidance in catheter directed thrombolysis (CDT) for acute limb ischaemia (ALI) has recently been dropped from European guidelines based on inconsistent literature. This study aimed to determine whether low fibrinogen levels and high activated partial thromboplastin time (APTT) are associated with an increased major bleeding risk during CDT.

METHODS

All consecutive patients treated with CDT for ALI in two Dutch hospitals between January 2004 and April 2021 were analysed retrospectively. Patients were treated with two dosing regimens (low dose: 50 000 IU/hour; high dose: 100 000 IU/hour) of urokinase and, after 2018, with a single low dose regimen of alteplase (rtPA) due to urokinase manufacturing problems. The incidence of major bleeding and associated APTT and fibrinogen levels were reviewed from patient charts.

RESULTS

Of the 443 included cases, 277 underwent CDT with urokinase and 166 with rtPA. The incidence of major bleeding in the whole cohort was 7%. Patients with a fibrinogen levels < 1.0 g/L developed more major bleeding than those in whom the fibrinogen level did not drop below 1.0 g/L (15% vs. 6%; p = .041). Systemic heparinisation during CDT or high (> 80 seconds) APTT were not significantly associated with major bleeding. Angiographic success (47% vs. 72%; p = .003) and 30 day amputation free survival (53% vs. 82%; p < .001) were lower for cases with major bleeding. Older age (odds ratio [OR] 1.06, 95% confidence interval [CI] 1.02 - 1.11), cardiac history (OR 3.35, 95% CI 1.39 - 8.06), high dose regimens (≥ 75 000 IU/hour urokinase; OR 2.67, 95% CI 1.18 - 6.04), and fibrinogen values < 1.0 g/L (OR 5.59, 95% CI 1.98 - 15.77) were independent predictors for major bleeding during CDT.

CONCLUSION

High dose thrombolytic regimens and fibrinogen levels of ≤ 1.0 g/L are associated with more major bleeding during thrombolytic therapy. Major bleeding significantly worsened the clinical outcome. A prospective comparative study is needed to assess the benefit of monitoring fibrinogen levels.

Direct delivery of plasmin using clot-anchoring thrombin-responsive nanoparticles for targeted fibrinolytic therapy

BACKGROUND

Fibrin-rich clot formation in thrombo-occlusive pathologies is currently treated by systemic administration of plasminogen activators (e.g. tPA), to convert fibrin-associated plasminogen to plasmin for fibrinolytic action. However, this conversion is not restricted to clot site only but also occurs on circulating plasminogen, causing systemic fibrinogenolysis and bleeding risks. To address this, past research has explored tPA delivery using clot-targeted nanoparticles.

OBJECTIVES

We designed a nanomedicine system that can (1) target clots via binding to activated platelets and fibrin, (2) package plasmin instead of tPA as a direct fibrinolytic agent, and (3) release this plasmin triggered by thrombin for clot-localized action.

METHODS

Clot-targeted thrombin-cleavable nanoparticles (CTNPs) were manufactured using self-assembly of peptide-lipid conjugates. Plasmin loading and its thrombin-triggered release from CTNPs were characterized by UV-visible spectroscopy. CTNP-targeting to clots under flow was studied using microfluidics. Fibrinolytic effect of CTNP-delivered plasmin was studied in vitro using BioFlux imaging and D-dimer analysis and in vivo in a zebrafish thrombosis model.

RESULTS

Plasmin-loaded CTNPs significantly bound to clots under shear flow and showed thrombin-triggered enhanced release of plasmin. BioFlux studies confirmed that thrombin-triggered plasmin released from CTNPs rendered fibrinolysis similar to free plasmin, further corroborated by D-dimer analysis. In the zebrafish model, CTNP-delivered plasmin accelerated time-to-recanalization, or completely prevented occlusion when infused before thrombus formation.

CONCLUSION

Considering that the very short circulation half-life (<1 second) of plasmin prevents its systemic use but also makes it safer without off-target drug effects, clot-targeted delivery of plasmin using CTNPs can enable safer and more efficacious fibrinolytic therapy.

In Vitro Blood Clot Formation and Dissolution for Testing New Stroke-Treatment Devices

Strokes are among the leading causes of death worldwide. Ischemic stroke, due to plaque or other buildup blocking blood flow to the brain, is the most common type. Although ischemic stroke is treatable, current methods have severe shortcomings with high mortality rates. Clot retrieval devices, for example, can result in physically damaged vessels and death. This study aims to create blood clots that are representative of those found in vivo and demonstrate a new method of removing them. Static blood clots were formed using a 9:1 ratio of whole sheep blood and 2.45% calcium chloride solution. This mixture was heated in a water bath at 37 °C for approximately one hour until solidified. Following clot solidification, human plasmin was introduced by various methods, including soaking, injection, and membrane perfusion, and the resulting dissolution percentages were determined. Different clot types, representative of the wide range found physiologically, were also manufactured and their dissolution characteristics evaluated. A method to reproducibly create blood clots, characteristic of those found in vivo, is essential for the production of stroke retrieval devices that can efficiently and effectively remove clots from patients with low mortality rates and little/no damage to the surrounding vessels.

Metal ion chelation enhances tissue plasminogen activator (tPA)-induced thrombolysis: an in vitro and in vivo study

Stroke is the third leading cause of death in the United States and the leading cause of adult disability. Despite enormous research efforts including many clinical trials, tissue plasminogen activator (tPA) remains the only FDA-approved treatment for acute ischemic stroke. Unfortunately, only 1-3% of stroke patients in the US receive this therapy because of the narrow time window and severe side effects for using tPA. The most deadly and damaging side effect is the risk of intracranial bleeding or hemorrhage. For that reason, the dose of tPA and its overall administration are under tight control, which may compromise the effect of thrombolysis. Studies have been focused on improving the effectiveness of tPA for higher rate of reperfusion, and the safety for less adverse bleeding episode. We studied how metal ions (zinc & iron) affect tPA-induced thrombolysis in vitro and in vivo, and proposed a method to improve the rate of thrombolysis. The amount of hemoglobin in the blood clot lysis was measured by a spectrophotometer. The tPA-induced thrombolysis was measured in vivo in femoral artery. Our results showed that Zn²⁺, Fe³⁺ and Fe²⁺ inhibited tPA-induced thrombolysis, with Zn²⁺ and Fe²⁺ being the most effective. Metal ion chelating agent EDTA when it was co-applied with tPA significantly enhanced the tPA-induced thrombolysis. The chelation alone did not have noticeable thrombolytic effect. In in vivo study of tPA-induced thrombosis following femoral artery thrombosis, the co-application of tPA and EDTA achieved significant higher rate of reperfusion than that by tPA treatment alone, suggesting that ion chelation facilitates tPA-induced thrombolysis and potentially improves the safety of tPA application by reducing the necessary dose of tPA application. Our results suggest that the co-application of a chelator and tPA improves the efficacy and, potentially, safety of tPA application, by reducing the necessary dose of tPA for thrombolysis.

Alpha2-Antiplasmin: The Devil You Don't Know in Cerebrovascular and Cardiovascular Disease

Alpha2-antiplasmin (α2AP), the fast-reacting, serine protease inhibitor (serpin) of plasmin, was originally thought to play a key role in protection against uncontrolled, plasmin-mediated proteolysis of coagulation factors and other molecules. However, studies of humans and mice with genetic deficiency of α2AP have expanded our understanding of this serpin, particularly in disease states. Epidemiology studies have shown an association between high α2AP levels and increased risk or poor outcome in cardiovascular diseases. Mechanistic studies in disease models indicate that α2AP stops the body's own fibrinolytic system from dissolving pathologic thrombi that cause venous thrombosis, pulmonary embolism, arterial thrombosis, and ischemic stroke. In addition, α2AP fosters the development of microvascular thrombosis and enhances matrix metalloproteinase-9 expression. Through these mechanisms and others, α2AP contributes to brain injury, hemorrhage and swelling in experimental ischemic stroke. Recent studies also show that α2AP is required for the development of stasis thrombosis by inhibiting the early activation of effective fibrinolysis. In this review, we will discuss the key role played by α2AP in controlling thrombosis and fibrinolysis and, we will consider its potential value as a therapeutic target in cardiovascular diseases and ischemic stroke.

Phase 2, randomized, open-label study on catheter-directed thrombolysis with plasmin versus rtPA and placebo in acute peripheral arterial occlusion

Background: Patients with acute peripheral arterial occlusion (aPAO) are candidates for operative thrombectomy, bypass, or catheter-directed thrombolysis (CDT) using a plasminogen activator. Human plasma-derived plasmin may offer another CDT option.

Objectives: To evaluate the efficacy, safety, and tolerability of two intrathrombus delivery methods and two doses of plasmin compared with recombinant tissue plasminogen activator (rtPA) and placebo in patients with aPAO.

Patients/methods: This was a phase 2, randomized, open-label study of intra-arterial CDT of plasmin in patients with aPAO. The study used infusion catheters with or without balloon occlusion (BOC) to evaluate 150 mg plasmin (2 and 5 h post-infusion) and 250 mg plasmin (5 h post-infusion). The efficacy of plasmin, rtPA and placebo was assessed.

Results: One hundred and seventy-four subjects were enrolled. Overall, the thrombolytic efficacy (>50% thrombolysis) was 59% (58/99) for 150 mg plasmin without BOC, which is comparable to 89% (8/9) for rtPA without BOC (p = 0.149) and 40% (2/5) for placebo control (p = 0.648). The thrombolytic efficacy was 33% of the 250 mg plasmin group. There was no difference (p > 0.999) in thrombolytic efficacy with BOC (59%, 58/99) or without BOC (59%, 17/29). Plasmin-treated groups experienced treatment-emergent adverse events (TEAEs) at 71% (76/107) without BOC and 63% (24/38) with BOC; 78% (7/9) of the rtPA-treated group and 89% (8/9) of the placebo group had TEAEs. Serious AEs (SAEs) occurred in 29% (31/107) of the 150 mg plasmin group without BOC and 24% (9/38) with BOC. No SAEs occurred in the 250 mg plasmin group.

Conclusions: Plasmin demonstrated less bleeding during catheter-directed administration at 150 mg and 250 mg doses compared to rtPA. BOC utilization did not improve efficacy. CDT with plasmin has a potential thrombolytic benefit in patients presenting with aPAO.

ClinicalTrials.gov Identifier: NCT01222117

Practice Trends of Fibrinogen Monitoring in Thrombolysis

There is a lack of evidence or societal guidelines regarding the utility of fibrinogen monitoring during thrombolysis. The purpose of our study was to investigate the current use of monitoring fibrinogen levels during thrombolysis. A voluntary, anonymous online survey was sent to all physician members of the Society of Interventional Radiology, consisting of 23 questions related to practitioner demographics, thrombolysis protocol, and fibrinogen monitoring. There were 455 physician responses; 82% of respondents monitored fibrinogen levels during thrombolysis, of which 97% decreased or stopped tissue plasminogen activator based on the level. Self-reported estimates of significant bleeding events during thrombolysis were 1.86% in those who monitored fibrinogen and 1.93% in those who did not. Only 34% of all respondents report, in their clinical experience, having found low fibrinogen level to be correlated with bleeding events. There was no significant difference in self-reported major bleeding rates between practitioners who monitor and those who do not monitor fibrinogen. This high variability of clinical use of fibrinogen monitoring during catheter-directed thrombolysis is secondary to the paucity of scientific studies demonstrating its utility; further scientific investigation is needed to define the true utility of fibrinogen monitoring.

Elevated Factor VIII and von Willebrand Factor Levels Predict Unfavorable Outcome in Stroke Patients Treated with Intravenous Thrombolysis

Introduction

Plasma factor VIII (FVIII) and von Willebrand factor (VWF) levels have been associated with the rate and severity of arterial thrombus formation and have been linked to outcomes following thrombolytic therapy in acute myocardial infarction patients. Here, we aimed to investigate FVIII and VWF levels during the course of thrombolysis in acute ischemic stroke (AIS) patients and to find out whether they predict long-term outcomes.

Materials and methods

Study population included 131 consecutive AIS patients (median age: 69 years, 60.3% men) who underwent i.v. thrombolysis with recombinant tissue plasminogen activator (rt-PA). Blood samples were taken on admission, 1 and 24 h after rt-PA administration to measure FVIII activity and VWF antigen levels. Neurological deficit of patients was determined according to the National Institutes of Health Stroke Scale (NIHSS). ASPECT scores were assessed using computer tomography images taken before and 24 h after thrombolysis. Intracranial hemorrhage was classified according to the European Cooperative Acute Stroke Study (ECASS) II criteria. Long-term functional outcome was determined at 90 days after the event by the modified Rankin scale (mRS).

Results

VWF levels on admission were significantly elevated in case of more severe AIS [median and IQR values: NIHSS <6:189.6% (151.9-233.2%); NIHSS 6-16: 199.6% (176.4-250.8%); NIHSS >16: 247.8% (199.9-353.8%), p = 0.013]; similar, but non-significant trend was observed for FVIII levels. FVIII and VWF levels correlated well on admission (r = 0.748, p < 0.001) but no significant correlation was found immediately after thrombolysis (r = 0.093, p = 0.299), most probably due to plasmin-mediated FVIII degradation. VWF levels at all investigated occasions and FVIII activity before and 24 h after thrombolysis were associated with worse 24 h post-lysis ASPECT scores. In a binary backward logistic regression analysis including age, gender, high-sensitivity C-reactive protein, active smoking, diabetes, and NIHSS >5 on admission, elevated FVIII and VWF levels after thrombolysis were independently associated with poor functional outcomes (mRS ≥ 3) at 90 days (immediately after thrombolysis: FVIII: OR: 7.10, 95% CI: 1.77-28.38, p = 0.006, VWF: OR: 6.31, 95% CI: 1.83-21.73, p = 0.003; 24 h after thrombolysis: FVIII: OR: 4.67, 95% CI: 1.42-15.38, p = 0.011, VWF: OR: 19.02, 95% CI: 1.94-186.99, p = 0.012).

Conclusion

Elevated FVIII activity and VWF antigen levels immediately after lysis and at 24 h post-therapy were shown to have independent prognostic values regarding poor functional outcomes at 90 days.

Antithrombotic Effect of Fermented Ophiopogon japonicus in Thrombosis-Induced Rat Models

In this study, the antithrombotic and thrombolytic ability of second fermented extract of Ophiopogon japonicus (FEOJ) was verified in thrombosis-induced rats. Thrombosis was induced by oral administration of 2% carrageenan for 4 weeks. Five experimental groups (n = 9/group) involved in the study were control group, thrombosis group, low-dose FEOJ group (2 mL/kg, low-dose Ophiopogon japonicus [LOJ]), middle-dose FEOJ group (6 mL/kg, medium-dose Ophiopogon japonicus [MOJ]), and high-dose FEOJ group (12 mL/kg, high-dose Ophiopogon japonicus [HOJ]). The clotting time (CT), bleeding time (BT), prothrombin time (PT), activated partial thromboplastin time (APTT), and fibrinogen (FBG) were assessed in blood samples, and histological studies were performed on liver and lung tissues. The results demonstrated delayed CT only in MOJ and HOJ groups and delayed BT in all FEOJ groups compared with those in thrombosis and control groups (P < .05). Similarly, APTT was significantly delayed only in MOJ and HOJ groups, and PT was significantly delayed in all FEOJ groups, compared with those in control and thrombosis groups (P < .05). Although concentrations of FBG were similar in control, thrombosis, and LOJ groups, the tendency for decreased concentration of FBG (statistically nonsignificant) in MOJ and HOJ groups has been observed. Histological examination of livers and lungs revealed that thrombosis was partially improved in FEOJ group compared with the thrombosis group. In conclusion, CT, BT, PT, and APTT were prolonged in FEOJ group more than in control and thrombosis groups, thereby, depicting antithrombotic and thrombolytic effects. However, concentration-dependent effects of FEOJ were more prominent in MOJ and HOJ groups than in the LOJ group.

Variable Resistance to Plasminogen Activator Initiated Fibrinolysis for Intermediate-Risk Pulmonary Embolism

Background

We examine the clinical significance and biomarkers of tissue plasminogen activator (tPA)-catalyzed clot lysis time (CLT) in patients with intermediate-risk pulmonary embolism (PE).

Methods

Platelet-poor, citrated plasma was obtained from patients with PE. Healthy age- and sex-matched patients served as disease-negative controls. Fibrinogen, α₂-antiplasmin, plasminogen, thrombin activatable fibrinolysis inhibitor (TAFI), plasminogen activator Inhibitor 1 (PAI-1), thrombin time and D-dimer were quantified. Clotting was induced using CaCl₂, tissue factor, and phospholipid. Lysis was induced using 60 ng/mL tPA. Time to 50% clot lysis (CLT) was assessed by both thromboelastography (TEG) and turbidimetry (A405).

Results

Compared with disease-negative controls, patients with PE exhibited significantly longer mean CLT on TEG (+2,580 seconds, 95% CI 1,380 to 3,720 sec). Patients with PE and a short CLT who were treated with tenecteplase had increased risk of bleeding, whereas those with long CLT had significantly worse exercise tolerance and psychometric testing for quality of life at 3 months. A multivariate stepwise removal regression model selected PAI-1 and TAFI as predictive biomarkers of CLT.

Conclusion

The CLT from TEG predicted increased risk of bleeding and clinical failure with tenecteplase treatment for intermediate-risk PE. Plasmatic PAI-1 and TAFI were independent predictors of CLT.

Plasmin-loaded echogenic liposomes for ultrasound-mediated thrombolysis

Plasmin, a direct fibrinolytic, shows a significantly superior hemostatic safety profile compared to recombinant tissue plasminogen activator (rtPA), the only FDA-approved thrombolytic for the treatment of acute ischemic stroke. The improved safety of plasmin is attributed to the rapid inhibition of free plasmin by endogenous plasmin inhibitors present in very high concentrations (1 μM). However, this rapid inhibition prevents the intravenous (IV) administration of plasmin. In emergency situations, catheter-based local administration is not practical. There is a need for an alternative technique for IV administration of plasmin. A possible solution is the encapsulation of plasmin in echogenic liposomes (ELIP) for protection from inhibitors until ultrasound (US)-triggered release at the clot site. ELIP are bilayer phospholipid vesicles with encapsulated gas microbubbles. US induces oscillation and collapse of the gas bubbles, which facilitates ELIP rupture and delivery of the encapsulated contents. Plasmin-loaded ELIP (PELIP) were manufactured and characterized for size, gas and drug encapsulations, and in vitro thrombolytic efficacy using a human whole blood clot model. Clots were exposed to PELIP with and without exposure to US (center frequency 120 kHz, pulse repetition frequency 1667 Hz, peak-to-peak pressure of 0.35 MPa, 50 % duty cycle). Thrombolytic efficacy was calculated by measuring the change in clot width over a 30-min treatment period using an edge detection MATLAB program. The mean clot lysis obtained with PELIP in the presence of US exposure was 31 % higher than that obtained without US exposure and 15 % higher than that obtained with rtPA treatment (p < 0.05).The enhanced clot lysis is attributed to the US-mediated release of plasmin from the liposomes.

Plasmin-dependent modulation of the blood-brain barrier: a major consideration during tPA-induced thrombolysis?

Plasmin, the principal downstream product of tissue-type plasminogen activator (tPA), is known for its potent fibrin-degrading capacity but is also recognized for many non-fibrinolytic activities. Curiously, plasmin has not been conclusively linked to blood-brain barrier (BBB) disruption during recombinant tPA (rtPA)-induced thrombolysis in ischemic stroke. This is surprising given the substantial involvement of tPA in the modulation of BBB permeability and the co-existence of tPA and plasminogen in both blood and brain throughout the ischemic event. Here, we review the work that argues a role for plasmin together with endogenous tPA or rtPA in BBB alteration, presenting the overall controversy around the topic yet creating a rational case for an involvement of plasmin in this process.

Fibrinogen Level as a Surrogate for the Outcome of Thrombolytic Therapy Using Tissue Plasminogen Activator for Acute Lower Extremity Intravascular Thrombosis

Purpose:

Monitoring of fibrinogen level is used to predict bleeding during lower extremity tissue plasminogen activator (tPA) infusions for peripheral arterial or venous thrombolysis. This practice is not fully addressed in the literature.

Materials and Methods:

We retrospectively reviewed fibrinogen levels and studied bleeding rate from charts of patients who underwent lower extremity tPA infusions at a single hospital from January 2010 to May 2012.

Results:

The rate of thrombolytic success did not correlate with fibrinogen level ( P = .53). The rate of major bleeding was significantly higher for patients with a fibrinogen level at or below 150 mg/dL ( P = .01). Patients whose tPA infusion was terminated within 46 hours had significantly lower rates of major bleeding ( P = .01) and thrombolytic failure ( P < .01). Periprocedural systolic blood pressure above 160 mm Hg was a risk factor for major bleeding ( P = .02). There was no association between concomitant aspirin use ( P = .90, .51) or hourly tPA dose ( P = .71, .62) and thrombolytic success or major bleeding, respectively.

Conclusion:

Fibrinogen level ≤150 mg/dL is associated with increased risk of major bleeding during tPA infusions. We suggest serial fibrinogen measurement as a viable method to monitor bleeding risk during lower extremity tPA infusions.

Protective effect of plasmin in marginal donor lungs in an ex vivo lung perfusion model

BACKGROUND

Donor lung thrombi are considered an important etiology for primary graft dysfunction in lung transplantation. We hypothesized that thrombolysis before lung transplantation could alleviate ischemia-reperfusion injury. This study was designed to evaluate the effect of the fibrinolytic agent plasmin on lungs damaged by thrombi in an ex vivo lung perfusion (EVLP) system.

METHODS

Rats were divided into control, non-plasmin, and plasmin groups (n = 7 each). In the control and plasmin groups, cardiac arrest was induced by withdrawal of mechanical ventilation without heparinization. Ventilation was restarted 150 minutes after cardiac arrest. The lungs were flushed, and the heart and lungs were excised en bloc. The lungs were perfused in the EVLP system for 60 minutes, and plasmin or placebo was administered upon EVLP initiation.

RESULTS

Fibrin/fibrinogen degradation products in the perfusate were significantly higher in the plasmin group than in the control and non-control groups (p < 0.001 for both). Plasmin administration significantly decreased pulmonary vascular resistance (plasmin vs non-plasmin, p = 0.011) and inhibited the exacerbation of dynamic compliance (plasmin vs non-plasmin, p = 0.003). Lung weight gain was less in the plasmin group than in the non-plasmin group (p = 0.04).

CONCLUSIONS

Our results confirmed that plasmin administration in an EVLP model dissolved thrombi in the lungs, resulting in reconditioning of the lungs as assessed by various physiologic parameters.

Thrombolytic, anticoagulant and antiplatelet activities of codiase, a bi-functional fibrinolytic enzyme from Codium fragile

Thrombosis is a leading cause of morbidity and mortality throughout the world. Thrombolytic agents are important for both the prevention and treatment of thrombosis. In this study, codiase, a new bi-functional fibrinolytic serine protease having thrombolytic, anticoagulant, and antiplatelet activities was purified from marine green alga, Codium fragile. The molecular weight of the enzyme was estimated to be 48.9 kDa by SDS-PAGE, and mass spectrometry. Fibrin zymography analysis showed an active band with similar molecular weight. The N-terminal sequence was found to be APKASTDQTLPL, which is different from that of other known fibrinolytic enzymes. Codiase displayed maximum activity at 30 °C and pH 6.0, and the activity was inhibited by Zn(2+) and Fe(2+). Moreover, the enzyme activity was strongly inhibited by serine protease inhibitor such as PMSF. Codiase exhibited high specificity for the substrate S-2288, and the Km and Vmax values for this substrate were found to be 0.24 mM and 79 U/ml respectively. Fibrin plate assays revealed that it was able to hydrolyze fibrin clot either directly or by activation of plasminogen. Codiase effectively hydrolyzed fibrin and fibrinogen, preferentially degrading α- and Aα chains, followed by γ-γ, and γ-chains. However, it provoked slower degradation of Bβ and β-chains. The structural change of fibrin clot and fibrinogen by codiase was also detected by FTIR-ATR spectroscopy analysis. In vitro and in vivo studies revealed that codiase reduces thrombosis in concentration-dependent manner. Codiase was found to prolong activated partial thromboplastin time (APTT), and prothrombin time (PT). PFA-100 studies showed that codiase prolonged the closure time (CT) of citrated whole human blood. These favorable antithrombotic profiles together with its anticoagulant and platelet disaggregation properties, and lack of toxicity to mice and NIH-3T3 cells, make it a potential agent for thrombolytic therapy.

Proteomics and transcriptome analysis coupled with pharmacological test reveals the diversity of anti-thrombosis proteins from the medicinal insect, Eupolyphaga sinensis

The insect of Eupolyphaga sinensis Walker has been used as traditional anti-thrombosis medicine without bleeding risk for several hundreds years in eastern countries. Our previous work has identified a bi-functional anti-thrombosis protein containing both direct-acting fibrin(ogen)olytic and plasminogen-activating activities from the insect. By proteomics and transcriptome analysis, 105 serine proteases belonging to four families were identified from the ground beetle, E. sinensis and the classification is for serine proteases of this organism. Pharmacological test indicated that 5 (eupolytin 1-5) of them have the abilities to hydrolyze fibrin(ogen) and/or activate plasminogen. The current work revealed the extreme diversity of anti-thrombosis components in E. sinensis and anti-thrombosis molecular mechanisms of the traditional medicinal insect, and provided many templates for the development of new thrombolytic agents. Especially, these proteins, which contain both plasmin- and PA (plasminogen-activating)-like activities, are excellent candidates for anti-thrombosis medicines.

Safety of catheter-delivered plasmin in patients with acute lower extremity arterial or bypass graft occlusion: phase I results

BACKGROUND

Current treatment of acute peripheral artery or bypass graft occlusion utilizes catheter-directed thrombolysis of a plasminogen activator (PA). Plasmin is a direct-acting thrombolytic with a striking safety advantage over PA in preclinical models.

OBJECTIVES

To report the first use of purified plasmin for acute lower extremity arterial or bypass graft thrombosis in a phase I dose-escalation study of a catheter-delivered agent.

METHODS

Eighty-three patients with non-embolic occlusion of infrainguinal native arteries or bypass grafts were enrolled (safety population) into seven sequential dose cohorts to receive 25-175 mg of plasmin by intrathrombus infusion over 5 h. Arteriograms were performed at baseline, 2 h, and 5 h, and subjects were monitored for 30 days for clinical outcomes and laboratory parameters of systemic fibrinolysis.

RESULTS

Major bleeding occurred in four patients (4.8%), and minor bleeding alone in 13 (15.7%), with no trend towards more bleeding at higher dosages of plasmin. There was a trend towards lower plasma concentrations of fibrinogen, α(2) -antiplasmin and α(2) -macroglobulin with increasing doses of plasmin, but the nadir fibrinogen concentration was > 350 mg dL(-1) at the highest plasmin dose. Individual nadir values were above 200 mg dL(-1) in 82 of 83 subjects, and were not different in patients with or without bleeding. Thrombolysis (≥ 50%) occurred in 79% of subjects receiving 125-175 mg of plasmin, as compared with 50% who received 25-100 mg.

CONCLUSIONS

Catheter-delivered plasmin can be safely administered to patients with acute lower extremity arterial occlusion at dosages of 25-175 mg.

Safety evaluation of a recombinant plasmin derivative lacking kringles 2-5 and rt-PA in a rat model of transient ischemic stroke

BACKGROUND

Tissue type plasminogen activator is the only approved thrombolytic agent for the treatment of ischemic stroke. However, it carries the disadvantage of a 10-fold increase in symptomatic and asymptomatic intracranial hemorrhage. A safer thrombolytic agent may improve patient prognosis and increase patient participation in thrombolytic treatment. A novel direct-acting thrombolytic agent, Δ(K2-K5) plasmin, promising an improved safety profile was examined for safety in the snare ligature model of stroke in the rat.

METHODS

Male spontaneously hypertensive rats were subjected to 6 hours middle cerebral artery occlusion followed by 18 hours reflow. Beginning 1 minute before reflow, they were dosed with saline, vehicle, Δ(K2-K5) plasmin (0.15, 0.5, 1.5, and 5 mg/kg) or recombinant tissue-type plasminogen activator (10 and 30 mg/kg) by local intra-arterial infusion lasting 10 to 60 minutes. The rats were assessed for bleeding score, infarct volume, modified Bederson score and general behavioral score. In a parallel study, temporal progression of infarct volume was determined. In an in vitro study, whole blood clots from humans, canines and rats were exposed to Δ(K2-K5). Clot lysis was monitored by absorbance at 280 nm.

RESULTS

The main focus of this study was intracranial hemorrhage safety. Δ(K2-K5) plasmin treatment at the highest dose caused no more intracranial hemorrhage than the lowest dose of recombinant tissue type plasminogen activator, but showed at least a 5-fold superior safety margin. Secondary results include: temporal infarct volume progression shows that the greatest expansion of infarct volume occurs within 2-3 hours of middle cerebral artery occlusion in the spontaneously hypertensive rat. A spike in infarct volume was observed at 6 hours ischemia with reflow. Δ(K2-K5) plasmin tended to reduce infarct volume and improve behavior compared to controls. In vitro data suggests that Δ(K2-K5) plasmin is equally effective at lysing clots from humans, canines and rats.

CONCLUSIONS

The superior intracranial hemorrhage safety profile of the direct-acting thrombolytic Δ(K2-K5) plasmin compared with recombinant tissue type plasminogen activator makes this agent a good candidate for clinical evaluation in the treatment of acute ischemic stroke.

Combination treatment with rt-PA is more effective than rt-PA alone in an in vitro human clot model

Incidence of intra-cranial hemorrhage linked to treatment of ischemic stroke with recombinant tissue plasminogen activator (rt-PA) has led to interest in adjuvant therapies such as ultrasound (US) or plasminogen, to enhance rt-PA efficacy and improve patient safety. High-frequency US (∼MHz) such as 2-MHz transcranial Doppler (TCD) has demonstrated increased recanalization in situ. Low-frequency US (∼kHz) enhanced thrombolysis (UET) has demonstrated higher lytic capabilities but has been associated with incidence of intracerebral hemorrhage in some clinical trials. In vitro studies using plasminogen have shown enhancement of lysis. This study compared rt-PA-induced lysis using adjuvant therapies, with 120-kHz or 2-MHz pulsed US, or plasminogen, in an in vitro human whole blood clot model. Blood was drawn from 30 subjects after local institutional approval. Clots were exposed to rt-PA at concentrations of 0 to 3.15 μg/ml. Clots were exposed to rt-PA alone (rt-PA) or in combination with plasminogen (Plg), 120-kHz US (120-kHz), or 2-MHz US (2-MHz). Thrombolytic efficacy was determined by assessing the percent fractional clot loss (FCL) at 30 minutes using microscopic imaging. There was no enhancement of lysis for combination therapy with [rt-PA]=0 μg/ml. Adding rt- PA increased lysis for all groups. As [rt-PA] increased, lysis tended to increase for 120-kHz and Plg (FCL: from 50% to 70%, 120-kHz; 65% to 83%, Plg) but not for 2-MHz (58% to 52%). Lytic efficacy in combination therapy depends on rt- PA concentration and the adjuvant therapy type. For non-zero rt-PA concentrations, all combination therapies produced more lysis than rt-PA alone.

Historical perspective and future direction of thrombolysis research: the re-discovery of plasmin

Two issues have held the focus of thrombolysis research for over 50 years, namely, choosing between a plasminogen activator (PA) or plasmin as the best therapeutic agent and choosing between systemic or local administration. The original plasmin product of the 1950s was both ineffective and contaminated with PA, and catheter technology was not yet developed for routine clinical use. For decades, clinical practice has focused on PA and systemic administration, but today, PAs are often administered by catheter into thrombosed vessels, notably for peripheral arterial and graft occlusion and deep vein thrombosis, and increasingly for acute ischaemic stroke. Despite using catheter-delivered therapy, bleeding complications still occur, most severely expressed as symptomatic intracranial haemorrhage. New experimental data indicate that we should now reconsider plasmin as a viable, even preferable, thrombolytic agent. Plasmin requires catheter delivery to achieve thrombolysis, but this technical issue has been solved with modern technology and widespread presence of interventional suites. After local administration, plasmin will lyse thrombi; thereafter, any plasmin in the circulation will be rapidly neutralised. Pre-clinical studies confirm that plasmin has marked haemostatic safety advantage over t-PA. After more than 50 years, the field has come full circle, and plasmin as the thrombolytic agent and catheter use for local delivery of agent may represent a step forward in thrombolytic therapy.

Comparison of plasmin with recombinant tissue-type plasminogen activator in lysis of cerebral thromboemboli retrieved from patients with acute ischemic stroke

BACKGROUND AND PURPOSE

Plasmin is a direct-acting thrombolytic with a better safety profile than recombinant tissue-type plasminogen activator (rtPA) in animal models. With the application of retrieval devices for managing acute ischemic stroke, extracted thromboemboli are available for ex vivo examination. We ask whether such thrombi are amenable to plasmin thrombolysis and whether such activity is different with rtPA.

METHODS

Thromboembolic fragments (total 29) were retrieved from the intracranial carotid artery system of 15 patients with acute ischemic stroke and randomly assigned to ex vivo thrombolysis with plasmin or rtPA. After an initial 2-hour exposure, residual material was exposed to the other agent for an additional 2 hours. Thrombolysis was quantified by change in thrombus area and released d-dimer.

RESULTS

Plasmin induced significant ex vivo thrombolysis of cerebral arterial thromboemboli, decreasing area by 45.9% ± 29.4% and 69.2% ± 52.5% and inducing median D-dimer release of 108,180 μg/L (range, 16,780 to 668,050 μg/L) and 16,905 μg/L (range, 240 to 403 085 μg/L) during the first and second 2-hour incubation periods, respectively. These changes were not different from those obtained with rtPA, which decreased area by 34.7% ± 57.8% (P=0.63) and by 68.4% ± 26.9% (P=0.97) and induced median D-dimer release of 151,990 μg/L (range, 9870 to 338,350 μg/L; P=0.51) and 34,520 μg/L (range 3794 to 325,400 μg/L; P=0.19) during the first and second 2-hour incubations.

CONCLUSIONS

Retrieved human cerebral thromboemboli were amenable to ex vivo lysis by plasmin, the rate and degree of which was not different than that achieved with rtPA.

Cytoprotective protein C pathways and implications for stroke and neurological disorders

Recent studies indicate that single-action-single-target agents are unlikely to cure CNS disorders sharing a pathogenic triad consisting of vascular damage, neuronal injury/neurodegeneration and neuroinflammation. Here we focus on a recent example of a multiple-action-multiple-target approach for CNS disorders based on newly discovered biological properties of activated protein C (APC), an endogenous plasma protease with antithrombotic, cytoprotective and anti-inflammatory activities in the CNS. We propose that APC-mediated signaling through the protease activated receptor-1 (PAR1) can favorably regulate multiple pathways within the neurovascular unit in non-neuronal cells and neurons during acute or chronic CNS insults, leading to stabilization of the blood-brain barrier (BBB), neuroprotection and control of neuroinflammation. Although much remains to be understood regarding the biology of APC, preclinical studies suggest that APC has promising applications as disease-modifying therapy for ischemic stroke and other neuropathologies whose underlying pathology involves deficits in the vasculo-neuronal-inflammatory triad.

A bi-functional anti-thrombosis protein containing both direct-acting fibrin(ogen)olytic and plasminogen-activating activities

Direct-acting fibrin(ogen)olytic agents such as plasmin have been proved to contain effective and safety thrombolytic potential. Unfortunately, plasmin is ineffective when administered by the intravenous route because it was neutralized by plasma antiplasmin. Direct-acting fibrin(ogen)olytic agents with resistance against antiplasmin will brighten the prospect of anti-thrombosis. As reported in 'Compendium of Materia Medica', the insect of Eupolyphaga sinensis Walker has been used as traditional anti-thrombosis medicine without bleeding risk for several hundreds years. Currently, we have identified a fibrin(ogen)olytic protein (Eupolytin1) containing both fibrin(ogen)olytic and plasminogen-activating (PA) activities from the beetle, E. sinensis.

OBJECTIVES

To investigate the role of native and recombinant eupolytin1 in fibrin(ogen)olytic and plasminogen-activating processes.

METHODS AND RESULTS

Using thrombus animal model, eupolytin1 was proved to contain strong and rapid thrombolytic ability and safety in vivo, which are better than that of urokinase. Most importantly, no bleeding complications were appeared even the intravenous dose up to 0.12 µmol/kg body weight (3 times of tested dose which could completely lyse experimental thrombi) in rabbits. It is the first report of thrombolytic agents containing both direct-acting fibrin(ogen)olytic and plasminogen-activating activities.

CONCLUSIONS

The study identified novel thrombolytic agent with prospecting clinical potential because of its bi-functional merits containing both plasmin- and PA-like activities and unique pharmacological kinetics in vivo.

Thrombolysis with plasmin: implications for stroke treatment

Plasmin is a direct-acting thrombolytic agent with a striking hemostatic safety advantage over plasminogen activators in animal models of thrombolysis and bleeding. In contradistinction to plasminogen activators, which risk bleeding at any effective thrombolytic dose, plasmin is tolerated without bleeding at several-fold higher amounts than those needed for thrombolysis. Plasmin has been safe in a current trial in patients with peripheral arterial or graft occlusion, and efforts are now directed toward therapy of stroke caused by cerebral artery occlusion. A rabbit (4 kg body weight) model of 2-hour, thrombin-induced middle cerebral artery occlusion using angiographic documentation of vascular patency and recanalization was used to perform a dose-ranging study of plasmin, delivered by catheter over a median duration of 10 minutes. Plasmin induced early recanalization in all animals (3 per group) within 10 minutes after discontinuation of 3, 2, or 1 mg of agent infusion. Control saline infusion failed to induce recanalization in 3 of 3 subjects. Plasmin rapidly induces middle cerebral artery recanalization, as determined in an angiogram-based animal model of arterial occlusion. Based on these data and other information, a phase I/IIa clinical trial of plasmin in human middle cerebral artery ischemic stroke has been initiated.

The fibrinolytic mechanism of defibrotide: effect of defibrotide on plasmin activity

Fibrinolytic activity has been shown to be reduced in many vascular diseases, including hepatic veno-occlusive disease after stem cell transplantation, a microangiopathy characterized by sinusoidal endothelial cell injury. Defibrotide is a polydisperse oligonucleotide with antithrombotic, profibrinolytic, anti-ischemic, and antiadhesive properties. Numerous clinical studies have shown promising activity of defibrotide in the treatment and prevention of veno-occlusive disease, with minimal toxicity. In corollary laboratory studies, defibrotide has been shown to decrease plasminogen activator inhibitor-1, increase tissue plasminogen activator levels, and increase overall plasma fibrinolytic activity in patients. Plasmin, a potent and nonspecific serine protease, plays a pivotal role in fibrinolysis by virtue of its ability to effectively degrade fibrin clots. In this study, defibrotide increases the activity of plasmin in hydrolyzing its substrate in a dose-dependent and length-dependent manner. Similar concentration-dependent effects of defibrotide were observed when plasmin was generated by tissue plasminogen activator or urokinase activation of plasminogen. In contrast, defibrotide had no direct effect on the activation of plasminogen to plasmin. Defibrotide was also able to enhance the activity of plasmin in degrading fibrin clot formed from fibrinogen, plasminogen, and thrombin. This effect was also concentration-dependent and directly correlated with the enzymatic activity of plasmin. This study therefore demonstrates that defibrotide is capable of enhancing the activity of plasmin and so contributes to its fibrinolytic activity. Taken together, these results support the effect of defibrotide in restoring the fibrinolytic vascular phenotype, in microangiopathic conditions such as veno-occlusive disease.

Direct fibrinolytic agents: biochemical attributes, preclinical foundation and clinical potential

Direct fibrinolytics are proteolytic enzymes that degrade fibrin without requiring an intermediate step of plasminogen activation. This review summarizes the current information available for five such agents, namely, plasmin (the prototypical form), three derivatives of plasmin (mini-plasmin, micro-plasmin, and delta-plasmin), and alfimeprase, a recombinant variant of a snake venom alpha-fibrinogenase, fibrolase. Biochemical attributes of molecular size, fibrin binding and inhibitor neutralization are compared. Preclinical investigations that assess the potential for thrombolytic efficacy in vitro and in animal models of vascular occlusion and for hemostatic safety in animal models of bleeding are detailed. Clinical potential has been assessed in patients with peripheral arterial and graft occlusion, acute ischemic stroke, and access catheter and hemodialysis shunt occlusions. The direct fibrinolytic agents have impressive biochemical and preclinical foundations for ultimate clinical application. However, clinical trial results for micro-plasmin and alfimeprase have not measured up to their anticipated benefit. Plasmin has thus far shown encouraging hemostatic safety, but efficacy data await completion of clinical trials. Whether direct fibrinolytics will provide clinical superiority in major thrombotic disorders over currently utilized indirect fibrinolytics such as tissue plasminogen activator remains to be determined.

Pre-clinical studies of plasmin: superior benefit-to-risk ratio of plasmin compared to tissue plasminogen activator

Currently-used thrombolytic agents are plasminogen activators (PA). While effective for treating thrombotic disease, PA use is associated with unavoidable hemorrhagic complications in susceptible individuals. Thus, there is an urgent need for new agents or approaches that provide greater hemostatic safety without sacrificing thrombolytic efficacy. Evidence now strongly indicates that 'direct-acting' thrombolytics, which do not require conversion of the precursor plasminogen to the active form plasmin, offer such a potential. The biochemical properties of plasmin provide a theoretical foundation for safe and effective therapy, based on thrombolytic efficacy upon local catheter delivery of agent and neutralization of circulating agent by its inhibitor (alpha-2 antiplasmin) to prevent bleeding complications. In vitro and animal studies support these predictions. In comparison with tissue-plasminogen activator (t-PA), plasmin shows a distinct benefit-to-risk advantage. First, plasmin is equally effective as t-PA in thrombolysis and may be superior for treating thrombi in totally-occluded vessels. Second, whereas t-PA causes bleeding from vascular trauma sites in animals when infused at dosages used for thrombolysis (0.5-1 mg/kg), plasmin exhibits safety at therapeutic dosages. In fact, plasmin can be used at several fold higher concentrations than is needed for thrombolysis, thereby providing a significant safety margin that is not attainable for t-PA or other PAs. Phase I trials with plasmin in hemodialysis graft occlusion and peripheral arterial occlusion have thus far confirmed the hemostatic safety of plasmin.

A first-in-human phase I trial of locally delivered human plasmin for hemodialysis graft occlusion

BACKGROUND

Hemodialysis (HD) grafts often fail because of stenosis at the venous anastomosis and thrombotic occlusion. Percutaneous management relies on thrombolysis with plasminogen activators, mechanical removal of thrombus, and angioplasty of the stenotic lesion.

OBJECTIVES

This report describes a phase I trial using Plasmin (Human) TAL 05-00018, a direct-acting fibrinolytic agent, to evaluate safety and, secondarily, to establish effective thrombolytic dosing.

PATIENTS/METHODS

Six cohorts of five patients with acute HD graft occlusion documented by angiography were treated with escalating dosages of plasmin (1, 2, 4, 8, 12, and 24 mg) infused over 30 min via criss-crossed pulse-spray catheters within the graft. The primary efficacy endpoint was > or =50% thrombolysis, as determined by comparison of pre-plasmin and 30-min post-plasmin fistulograms.

RESULTS

Of 31 subjects who received study drug (safety population), one withdrew and 30 completed the trial (evaluable for efficacy). There was no significant change in plasma alpha-2 antiplasmin or fibrinogen concentration, major bleeding did not occur, and there were no deaths. Serious adverse events in four patients were not related to the study drug. There was a dose-response relationship for the primary efficacy endpoint, all five subjects receiving 24 mg achieving >75% lysis.

CONCLUSIONS

This first phase I study of Plasmin (Human) TAL 05-00018, infused into thrombosed HD grafts, documents safety at dosages of 1-24 mg and an effective thrombolytic dosage of 24 mg. The results establish a foundation for further clinical study of catheter-based plasmin administration in thrombotic disorders.

Middle cerebral artery occlusion in the rabbit using selective angiography: application for assessment of thrombolysis

BACKGROUND AND PURPOSE

An animal model of selective middle cerebral artery (MCA) occlusion is needed for evaluation of intra-arterial (IA) delivery of thrombolytic agents. We describe a technique for MCA thrombo-occlusion in the rabbit with real-time angiographic documentation of occlusion and thrombolytic recanalization.

METHODS

After femoral artery cutdown, a microcatheter was advanced from the internal carotid artery to the MCA. MCA occlusion was achieved by IA thrombin and reperfusion by IA plasmin.

RESULTS

The terminal internal carotid artery was successfully catheterized in 12 of 13 animals. Stable (2-hour) MCA occlusion was induced and verified angiographically in all 12 animals; 2 animals also had distal internal carotid artery thrombus. Recanalization was achieved rapidly after IA plasmin in 3 of 3 animals.

CONCLUSIONS

We describe a new animal model of selective MCA occlusion documented by real-time angiography and used to demonstrate recanalization with IA plasmin.

Microplasmin and tissue plasminogen activator: comparison of therapeutic effects in rat stroke model at multiparametric MR imaging

PURPOSE

To prospectively compare therapeutic and hemorrhagic effects of microplasmin and tissue plasminogen activator (tPA) in stroke therapy by using multiparametric magnetic resonance (MR) imaging in a photothrombotic rat stroke model.

MATERIALS AND METHODS

The animal experiment complied with institutional regulations for laboratory animals. Stroke was induced in rats with photothrombotic occlusion of middle cerebral artery (MCA). T2-weighted, perfusion-weighted (PW), and diffusion-weighted (DW) MR imaging was performed 1 hour and 24 hours after occlusion. On the basis of PW and DW images at 1 hour, 49 rats with cortex and subcortex involvement and with perfusion-diffusion mismatch were randomly assigned into one of four groups: control group, group treated with 7.5 mg microplasmin, group treated with 10 mg/kg microplasmin, or group treated with 10 mg/kg tPA. Agents were intravenously injected 1.5 hours after occlusion. Infarct size and hemorrhagic transformation were assessed with MR imaging and histomorphologic findings. Neurologic deficit was scored. Measurements were statistically analyzed.

RESULTS

There were 13 rats in the control group, 13 in the 7.5 mg/kg microplasmin group, nine in the 10 mg/kg microplasmin group, and 14 in the 10 mg/kg tPA group. Despite similar baseline perfusion-diffusion mismatch, histochemically defined total infarct volume was reduced from 25% +/- 5 (standard deviation) in control group to 21% +/- 2, 20% +/- 4, and 20% +/- 5 in 7.5 mg/kg microplasmin, 10 mg/kg microplasmin, and tPA groups, respectively, as similarly shown on T2-weighted, DW, and PW images at 24 hours (P < .05). Cerebral hemorrhage rate at 24 hours was higher in tPA group than in the other three groups. Bederson score of neurologic deficits was significantly reduced in treated groups compared with that in control group.

CONCLUSION

Perfusion-diffusion mismatch appeared useful in selecting candidates for thrombolytic therapy. Multiparametric MR imaging allowed noninvasive assessment of effects of microplasmin and tPA in rats; microplasmin had a significantly lower hemorrhagic rate.

Blood inhibitory capacity toward exogenous plasmin

Stabilized, active plasmin is a novel thrombolytic for direct delivery to clots. Although it is known that protease inhibitors in plasma inhibit plasmin, the amount of plasmin that can be added to plasma/blood before free plasmin is observed is not clear. Determination of free plasmin activity in plasma using chromogenic substrates represents a challenge due to false-positive signals from plasmin entrapped by alpha2-macroglobulin. Size-exclusion chromatography was used to separate the plasmin-alpha2-macroglobulin complex from uninhibited, free plasmin. In this in-vitro study, exogenous plasmin is effectively inhibited up to 2.4 micromol/l after 5-min incubation with plasma at 37 degrees C. Initially, plasmin was consumed predominantly by alpha2-antiplasmin up to 1.2 micromol/l plasmin. Following exhaustion of alpha2-antiplasmin, plasmin was further consumed by alpha2-macroglobulin up to 2.4 micromol/l plasmin added to human plasma. Whole human blood was found to have an increased inhibitory capacity over that of plasma; free plasmin activity could be measured only above 3.8 micromol/l added plasmin. In conclusion, several mechanisms exist that control plasmin activity in human blood; in addition to alpha2-antiplasmin and alpha2-macroglobulin, blood cells contribute to the inhibition of exogenously administered plasmin. These in-vitro results indicate that doses of plasmin up to approximately 12 mg/kg in humans can be completely inactivated by blood.

Independent contributions of hypothermia and acidosis to coagulopathy in swine

BACKGROUND

Clinical coagulopathy occurs frequently in the presence of acidosis and hypothermia. The purpose of this study was to determine the relative contributions of acidosis and hypothermia to coagulopathy, as measured by current standard bedside and clinical laboratory analyses (i.e., bleeding time and prothrombin time). In addition, we investigated possible mechanisms of these effects using a modified prothrombin time test, thromboelastography, and thrombin kinetics analyses. An improved understanding of coagulopathy should facilitate hemorrhage control.

METHODS

Twenty-four pigs were randomly allocated into normal (pH, 7.4; 39 degrees C), acidotic (pH, 7.1; 39 degrees C), hypothermic (pH, 7.4; 32 degrees C), and acidotic and hypothermic (pH, 7.1; 32 degrees C) combined groups. Acidosis was induced by the infusion of 0.2N hydrochloric acid in lactated Ringer's solution. Hypothermia was induced by using a blanket with circulating water at 4 degrees C. Development of a clinical coagulopathy was defined as a significant increase in splenic bleeding time. Measurements were compared before (pre) and 10 minutes after (post) the target condition was achieved.

RESULTS

Acidosis, hypothermia, or both caused the development of coagulopathy, as indicated by 47%, 57%, and 72% increases in splenic bleeding time (p < 0.05, pre vs. post). Plasma fibrinogen concentration was decreased by 18% and 17% in the acidotic and combined groups, respectively, but not in the hypothermic group. Hypothermia caused a delay in the onset of thrombin generation, whereas acidosis primarily caused a decrease in thrombin generation rates. At 4 minutes' quench time, thrombin generation in the acidotic, hypothermic, and combined groups were 47.0%, 12.5%, and 5.7%, respectively, of the value in the control group. There were no changes in serum tumor necrosis factor-alpha and interleukin-6 in any group during the study.

CONCLUSION

Acidosis and hypothermia cause a clinical coagulopathy with different thrombin generation kinetics. These results confirm the need to prevent or correct hypothermia and acidosis and indicate the need for improved techniques to monitor coagulopathy in the trauma population.

Cross-Species Pharmacologic Evaluation of Plasmin as a Direct-Acting Thrombolytic Agent: Ex Vivo Evaluation for Large Animal Model Development

PURPOSE

Human plasma-derived plasmin has been developed for the treatment of thrombosed hemodialysis arteriovenous grafts and vascular occlusive diseases. To further investigate this drug in large animal models and derive preliminary dosing estimates, the authors compared plasmin's relative lytic potential in four species, including man. The goal was to find which species' whole blood clots best compared to human clots in terms of lysis with plasmin. The results from these studies will serve to guide species selection for large animal experimentation.

MATERIALS AND METHODS

Clotted blood from human, pig, sheep, and bovine subjects were treated with saline solution control, plasmin, or tissue plasminogen activator. Electron microscopy (EM) techniques were used to investigate the effects of clot size and fragmentation on plasmin lysis, the effects of intrathrombic infusion by injection of plasmin directly into whole blood clots, and species fibrin structural differences.

RESULTS

Under static conditions, plasmin efficiently lysed clots from all species studied at an optimal dose of 4-5 mg per 4-5 g of clot. With fragmented human clots, plasmin (5 mg)-induced lysis was 80% +/- 2% at 60 minutes. Porcine clots were more resistant to plasmin lysis compared with human, ovine, and bovine clots. Percent lysis at 60 minutes with plasmin for ovine clots was 72% +/- 3% (4-mg dose), compared with 50% +/- 4% for porcine clots (5-mg dose; P < .05). EM of porcine clots showed a compact fibrin network that appeared more dense than that in human or sheep clots, which may account for the decreased lytic rate.

CONCLUSIONS

Human plasmin is an effective direct-acting thrombolytic agent that is capable of lysing fibrin from several species. Ex vivo lysis studies were used to investigate the most appropriate large animal model that best approximates plasmin lysis with human clots under certain conditions. It was determined that ovine clots treated with plasmin most closely resemble the lysis observed with human clots.

Thrombolytic activity of BB-10153, a thrombin-activatable plasminogen

BACKGROUND

BB-10153 is an engineered variant of human plasminogen, modified to be activated to plasmin by thrombin. Thrombin-activatable plasminogen was designed as a novel thrombolytic agent which would persist in the blood as a prodrug and be activated to plasmin only at fresh or forming thrombi by the thrombin that is tightly localized there. We previously described the construction of several thrombin-activatable plasminogens and their in vitro clot lysis activity.

OBJECTIVES AND METHODS

The current study was an examination of the thrombolytic properties of BB-10153 in vivo; comparison was made with tissue-type plasminogen activator (t-PA) in a femoral artery copper coil thrombosis model in the anesthetized dog and rabbit. Heparin was not coadministered so that the fundamental activity of the agents could be compared.

RESULTS

BB-10153, administered as an intravenous bolus of 5 mg kg(-1) in the dog and 10 mg kg(-1) in the rabbit, produced a comparable incidence of reperfusion to 3 mg kg(-1) t-PA. Reocclusion at these doses occurred in 4/4 dogs and 5/7 rabbits treated with t-PA and in 2/6 dogs and 0/10 rabbits treated with BB-10153. There was no reocclusion in three dogs dosed with 10 mg kg(-1) BB-10153. BB-10153 did not affect plasma alpha2-antiplasmin levels or the bleeding time, whereas 3 mg kg(-1) t-PA caused marked depletion of alpha2-antiplasmin and fibrinogen and increased the bleeding time. The plasma half-life of BB-10153 was 3-4 h.

CONCLUSIONS

The long half-life and thrombus-selective thrombolytic activity of BB-10153 might allow it to overcome the bleeding and reocclusion shortfalls in the performance of current thrombolytics.

Locally delivered plasmin: why should it be superior to plasminogen activators for direct thrombolysis?

With advances in the field of thrombolytic therapy, whereby clots are routinely treated locally via a catheter, traditional systemic thrombolytics such as plasminogen activators might not be the best drugs for this task. Plasmin represents a new class of thrombolytic agents that exhibit direct fibrinolytic activity, without the need for either plasminogen or a plasminogen activator. In contrast to plasminogen activators, this independence from plasminogen allows plasmin to efficiently dissolve long, retracted blood clots that are inherently deficient in plasminogen. Preclinical safety studies in rabbits demonstrate that plasmin, in contrast to tissue-type plasminogen activator, does not cause re-bleeding from preformed hemostatic plugs. These results predict that plasmin will prove to be both superior to, and safer than, plasminogen activators in the dissolution of long, retracted blood clots in humans.

Involvement of Thrombolysis in Recombinant Tissue Plasminogen Activator-Induced Cerebral Hemorrhages and Effect on Infarct Volume and Postischemic Endothelial Function

Background and Purpose— In a model of mechanical focal ischemia, we investigated the involvement of thrombolysis products (TLP) in recombinant tissue plasminogen activator (rtPA)-induced intracerebral complications and the effects on infarct volume and postischemic endothelial function.

Methods— Hemorrhage incidence and severity were evaluated by histomorphometric analysis in male spontaneously hypertensive rats (SHR) subjected to 60-minute intraluminal middle cerebral artery (MCA) occlusion and receiving intravenously 5 hours later either saline, rtPA (3, 10, or 30 mg/kg), or rtPA (10 mg/kg) associated with TLP (rtPA+TLP). In addition, MCA reactivity was assessed in rtPA- or rtPA+TLP-treated SHR versus control Wistar-Kyoto rats or SHR.

Results— No hemorrhage was observed visually in SHR receiving saline. In contrast, rtPA administration induced hemorrhagic complications in infarcted areas in a dose-independent manner. Administration of rtPA+TLP solution, containing a high concentration of plasmin, did not affect hemorrhage incidence but significantly increased hemorrhage severity (8.8±2.3 petechiae versus 3.0±1.0 petechiae in rtPA group; P <0.001). This increased severity was associated with a significant increase of both infarct volume (182±10 versus 144±15 mm 3 in rtPA group; P <0.01) and postischemic impairment of MCA endothelium-dependent relaxation (9±0.5% versus 13±1% in rtPA group; P <0.05).

Conclusions— Treatment with rtPA led to intracerebral hemorrhages, in contrast to saline-treated animals, and the presence of TLP increased the severity of these hemorrhages, in parallel with increased infarct volume and worsened endothelial function.