Enhanced clot lysis by a single point mutation in a reteplase variant

Recombinant tissue-type plasminogen activator (rtPA) is the clot lysis drug approved for clinical use, and is characterised by a short half-life and substantial inactivation by plasminogen activator inhibitor-1 (PAI-1). We previously discovered that a tPA mutation (A419Y) at the protease domain led to enhanced fibrinolysis activity. In the present study, we studied the mechanism of such mutation in enhancing the proteolytic activity, and whether such enhancement persists in reteplase, an United States Food and Drug Administration-approved tPA truncated variant. We constructed and expressed a series of reteplase-based mutants, including rPA^G (glycosylated rPA), rPA^G -Y (with A419Y mutant at rPA^G ), rPA^G -A4 (tetra-alanine mutation at 37-loop of rPA^G ), and rPA^G -A4/Y (with both) and evaluated their plasminogen activation and PAI-1 resistance. Surface plasmon resonance analysis showed that the rPA^G had fibrin affinity comparable to full-length tPA. Moreover, rPA^G -Y had 8·5-fold higher plasminogen activation and stronger tolerance to PAI-1 compared to rPA^G . We also found that the mutations containing tetra-alanine (rPA^G -A4 and rPA^G -A4/Y) had dramatically reduced plasminogen activation and impaired clot lysis. In a pulmonary embolism murine model, rPA^G -Y displayed a more efficient thrombolytic effect than rPA^G . These results identified a novel mutant reteplase variant of tPA with increased fibrinolytic activity, laying the foundation for the development of a new potent fibrinolytic agent.

Efficacy of modified pressure cuff for thrombolytic treatment on lower extremity deep venous thrombosis

ABSTRACT

To compare the effectiveness and patient comfort between two methods that block superficial venous blood flow during the thrombolytic treatment of lower extremity deep venous thrombosis (DVT) to provide evidence that informs clinical choice.One hundred twenty patients with lower extremity DVT were randomly divided into sphygmomanometer (group A, n = 40), tourniquet (group B, n = 40), and control group (no blocking, n = 40). All the patients were treated with a daily dosage of urokinase using a dial sphygmomanometer cuff and tourniquet to block lower extremity superficial vein blood flow. The pressure of the dial sphygmomanometer blocking lower extremity superficial vein blood flow was measured during lower extremity venography. Leg swelling reduction rate, venous patency, thrombus removal rate, and average comfort index were observed during the blocking process.The average pressure value for group A was 70  ± 10 mm Hg. The differences in the swelling reduction rate and venous patency were significant between the groups. Comparing the two groups at different time points, the average thrombus clearance rate of group A was higher than that of group B and control group. The leg pain scores of group A were lower than those of group B and control group. The postoperative comfort ratio of group A was higher than that of group B, and the proportion of severe discomfort in group A was lower than that in group B.Compared with the tourniquet, using a dial sphygmomanometer cuff to block lower extremity superficial vein blood flow achieved a better thrombolytic effect on DVT and provided higher patient comfort during treatment.

Feasibility of low-dose infusion of alteplase for unsuccessful thrombolysis with urokinase in deep venous thrombosis

The aim of the present study was to investigate whether the rescue of thrombolysis with the recombinant tissue plasminogen activator (rt-PA) alteplase was an effective and safe therapeutic option in patients who did not respond to urokinase. Between February 2016 and February 2017, 26 patients with deep venous thrombosis (DVT) underwent rescue thrombolysis with alteplase. Unsuccessful thrombolysis with urokinase was defined as a lack of improvement in the degree of thrombotic removal with a lysis rate <50% under one of the following three conditions: Two consecutive venography procedures, administration of >3 million units of total urokinase, or >7 days infusion duration. The thrombus score, lysis rate and post-thrombolysis safety of alteplase, following unsuccessful urokinase thrombolysis were all evaluated. At the end of the unsuccessful urokinase thrombolytic therapy, the mean duration of the perfusion was 6.09±1.60 days, and the mean total dose was (362.5±90.0) ×10⁴ units. No significant difference was detected in the total thrombus score before (7.85±2.40) and at the completion (6.19±2.33) of urokinase thrombolysis (P>0.05). The mean duration of perfusion was 3.36±1.69 days, and the mean total infusion dose was 44.8±22.6 mg for the rescue thrombolysis with alteplase. The mean thrombus score decreased to 1.19±2.10 at the completion of rescue thrombolysis. The alteplase post-thrombolysis scores were significantly decreased compared with those of urokinase thrombolysis (P<0.05). There were 23 (88.5%) patients who achieved a successful lysis rate (grade II/III) following rescue thrombolysis with alteplase, and symptoms of swelling and pain in the affected limbs were significantly improved. Successful thrombolysis rates in patients in the acute (<14 days) and subacute (14-28 days) phases were high (93.3 and 81.8%, respectively; P>0.05). No symptomatic pulmonary embolism or major bleeding occurred during rescue thrombolysis, but minor bleeding complications occurred in 4 cases (15.4%). In conclusion, rescue thrombolysis with alteplase led to an effective and safe outcome in patients with DVT who did not respond to initial thrombolysis with urokinase, and may be a valid and easy alternative treatment option.

Pharmacomechanical thrombolysis with a rotator thrombolysis device in iliofemoral deep venous thrombosis

OBJECTIVE

Deep venous thrombosis (DVT) is a life-threatening and morbid pathology. This study aimed to investigate the efficacy of an early thrombolysis procedure using a rotator thrombolysis device.

METHODS

Sixty-seven patients with acute proximal DVT were enrolled in the study. Patients' data were recorded retrospectively. Initially, an infrarenal retrievable vena cava filter was placed through the femoral vein. Then, a rotator thrombolysis device and a thrombolytic agent injection were applied to the occluded segments of the deep veins by puncturing the popliteal vein.

RESULTS

The identified reasons were trauma (43.3%), pregnancy (20.9%), undiagnosed (11.9%), major surgical operation (10.5%), immobilization (7.5%), and malignancy (5.9%). Immediate total recanalization was conducted in all patients, and the leg diameters returned to normal ranges in the early postoperative period. Hospital mortality or severe complications were not detected.

CONCLUSION

New thrombolytic devices seem to reduce in-hospital mortality risks and may potentially decrease post-thrombotic morbidity.

Direct microscopic monitoring of initial and dynamic clot lysis using plasmin or rt-PA in an in vitro flow system

INTRODUCTION

Plasmin is a direct-acting thrombolytic agent with a favorable safety profile upon intra-arterial delivery in pre-clinical and phase I studies. However, the thrombolytic efficacy of plasmin, relative to that of rt-PA, remains to be established. We have compared the dynamics of clot lysis with plasmin or rt-PA in an in vitro perfusion system, in which thrombolytic agent is administered locally, allowed to induce lysis for short intervals, then washed with plasma in a re-circulation circuit.

MATERIALS AND METHODS

Whole blood human clots were prepared in observation chambers, exposed to plasmin or rt-PA at equimolar concentrations (1.2/1.0, 1.8/1.5 and 2.4/2.0 mg/ml) for measured intervals of time, followed by perfusion with human plasma. Clot size was monitored by digital analysis of sequential photographs obtained through an optical microscope.

RESULTS

Plasma perfusion after incubation with thrombolytic agent rapidly removed superficial clot fragments. This initial decrease in clot size was greater with plasmin than with rt-PA when tested at the highest concentrations of agent (0.63 ± 0.11 vs. 0.30 ± 0.11, p=0.001 for clots with non-cross-linked fibrin and 0.53 ± 0.15 vs. 0.14 ± 0.15, p=0.02, for clots with cross-linked-fibrin). Subsequent clot lysis during plasma flow was greater after prior incubation with rt-PA. Longer incubation times of plasmin resulted in larger portions of the clot being washed free. Repeated plasmin incubations and plasma perfusions of a clot successfully induced stepwise reductions in clot size.

CONCLUSIONS

Initial clot lysis is greater with direct exposure using plasmin than rt-PA. During washout and circulation with plasma, rt-PA induced continued clot lysis, while plasmin lysis was curtailed, presumably because of plasmin inhibition.

Biochemical dynamics relevant to the safety of low-dose, intraclot alteplase for deep vein thrombosis

Intraclot tissue plasminogen activator (tPA) has been shown to be an effective treatment for deep vein thrombosis (DVT) (Radiology 2008;246:619 and J Vasc Interv Radiol 2011;22:1107). We sought to correlate pharmacokinetics of tPA, fibrinogen, fibrinolytic inhibitors, and D-dimers with the safety and efficacy of intraclot tPA. Thirty subjects received intraclot tPA for lower extremity DVT by infiltrating the thrombus with ≤10 mg doses tPA in an open-label study, using a pulse-spray catheter. We measured various parameters over 8 h following a first dose of tPA. Mean tPA levels of 75 units per mL (95% confidence interval 19-131 units/mL) were seen immediately after administration of a mean tPA dose of 8.0 mg (SD 1.5 mg). tPA levels returned to baseline within 2 h of completion of treatment. Plasminogen activator inhibitor-1 (PAI-1) was consumed following tPA treatment, but rose to levels significantly greater than baseline (P < 0.001). Fibrinogen decreased slightly, but remained >125 mg/dL for all subjects. α2-antiplasmin decreased from a mean of 115 units/mL to 56 units/mL after tPA administration (P < 0.001) and remained decreased for 8 h. Plasminogen at baseline (112 units/mL) decreased to 89 units/mL immediately after tPA administration (P < 0.001) and was unchanged thereafter. D-dimer levels were >20 μg/mL in all but 4 subjects, one of whom was the only one to fail to achieve clot lysis. The safety of low-dose, intraclot tPA is due to its short persistence in the circulation, lack of hypofibrinogenemia, and a reflexive rise of PAI-1. Subjects whose D-dimers remain <20 μg/mL are at risk of not achieving thrombolysis.

Case study and review: treatment of tricuspid prosthetic valve thrombosis

Prosthetic valve thrombosis (PVT) is a severe and life-threatening complication of heart valve replacement. Conventional therapy is surgical thrombectomy or valve replacement. Medical thrombolysis is another emerging option. We report the case of a 57 year old woman with a history of Ebstein anomaly who underwent successful treatment of tricuspid prosthetic valve thrombosis with intra-atrial infusion of very low dose recombinant tissue plasminogen activator (tPA). We review the presentation, etiology, diagnosis, and treatment of tricuspid PVT emphasizing a modified medical option as a safe, minimally invasive alternative to surgical intervention or conventional medical therapy for tricuspid valve thrombosis.

Low-dose, once-daily, intraclot injections of alteplase for treatment of acute deep venous thrombosis

PURPOSE

To evaluate the safety and efficacy of once-daily intraclot injections of low doses (≤ 10 mg) of tissue plasminogen activator (tPA) for thrombolysis of venous thrombosis.

MATERIALS AND METHODS

In prospective studies, 33 patients with subclavian, jugular, and central venous thrombosis (SJ-CVT) (all but two cases associated with central catheters) were treated once a day with ≤ 4 mg/day of tPA, and 30 patients with acute deep vein thrombosis of the lower extremity (DVT-LE) < 14 days old were treated once a day with ≤ 10 mg/leg/day of tPA by intraclot "lacing" of thrombus without continuous infusions of tPA.

RESULTS

Patency was restored in 26 (79%) of 33 patients with SJ-CVT using an average total dose of 7.1 mg of tPA/per patient and average of 2.1 treatments or days of therapy. Five patients received thrombolytic therapy for SJ-CVT as outpatients. Initial patency was restored in 29 (97%) of 30 patients with acute DVT-LE using an average total dose of 20 mg of tPA per patient over an average of 2.7 treatments/or days per patient. Follow-up imaging examinations at 6 months showed continued patency in 27 (96%)/of 28 patients. There were no major bleeding complications, and no patient required a blood transfusion.

CONCLUSIONS

Intraclot injection of low doses of alteplase is effective for acute venous thrombosis, and pharmacokinetic data suggest potentially greater safety.

Catheter-directed thrombolysis of lower limb thrombosis

Late complications of thrombosis of the deep veins in the region between the popliteal vein termination and the confluence of the common iliac veins and inferior vena cava (suprapopliteal deep-vein thrombosis) are common and often unrecognized by those responsible for the initial management. Pharmacomechanical-assisted clearance of the thrombus at the time of first presentation provides the best opportunity for complete recovery with preservation of normal venous valve function and avoidance of recurrent deep-vein thrombosis and postthrombotic syndrome. Recent interventional radiology methods provide for rapid and complete thrombolysis even in some patients in whom thrombolysis was previously considered contraindicated. This review describes the methods, safety, and efficacy of acute interventional treatment of suprapopliteal deep-vein thrombosis.

Catheter-directed thrombolysis vs. anticoagulant therapy alone in deep vein thrombosis: results of an open randomized, controlled trial reporting on short-term patency

BACKGROUND

Approximately one in four patients with acute proximal deep vein thrombosis (DVT) given anticoagulation and compression therapy develop post-thrombotic syndrome (PTS). Accelerated removal of thrombus by thrombolytic agents may increase patency and prevent PTS.

OBJECTIVES

To assess short-term efficacy of additional catheter-directed thrombolysis (CDT) compared with standard treatment alone.

PATIENTS AND METHODS

Open, multicenter, randomized, controlled trial. Patients (18-75 years) with iliofemoral DVT and symptoms < 21 days were randomized to receive additional CDT or standard treatment alone. After 6 months, iliofemoral patency was investigated using duplex ultrasound and air-plethysmography assessed by an investigator blinded to previous treatment.

RESULTS

One hundred and three patients (64 men, mean age 52 years) were allocated additional CDT (n = 50) or standard treatment alone (n = 53). After CDT, grade III (complete) lysis was achieved in 24 and grade II (50%-90%) lysis in 20 patients. One patient suffered major bleeding and two had clinically relevant bleeding related to the CDT procedure. After 6 months, iliofemoral patency was found in 32 (64.0%) in the CDT group vs. 19 (35.8%) controls, corresponding to an absolute risk reduction (RR) of 28.2% (95% CI: 9.7%-46.7%; P = 0.004). Venous obstruction was found in 10 (20.0%) in the CDT group vs. 26 (49.1%) controls; absolute RR 29.1% (95% CI: 20.0%-38.0%; P = 0.004). Femoral venous insufficiency did not differ between the two groups.

CONCLUSIONS

After 6 months, additional CDT increased iliofemoral patency from 36% to 64%. The ongoing long-term follow-up of this study will document whether patency is related to improved functional outcome.