Pharmacokinetics and thrombolytic effects of the recombinant tissue-type plasminogen activator in horses

Ex Vivo Machine Thrombolysis Reduces Rethrombosis Rates in Salvaged Thrombosed Myocutaneous Flaps in Swine

BACKGROUND

There is a risk for thrombotic complications (2 to 5 percent) associated with microsurgical reconstruction. Current thrombolytic therapy has a salvage rate between 60 and 70 percent, but it is afflicted by bleeding complications (2 to 6 percent). The use of machine perfusion for delivering thrombolytic agents is a new method that could potentially reduce these complications. In this article, the authors compared flap salvage outcomes comparing machine thrombolysis versus a manual flush with tissue plasminogen activator.

METHODS

Sixteen bilateral flaps (12 × 9 cm) were dissected from eight female Dutch Landrace pigs (70 kg). Thrombosis was induced in free rectus abdominis flaps by clamping the pedicle's veins for 2 hours. Flaps were either thrombolysed with 2 mg tissue plasminogen activator (1 mg/ml) during 2 hours of machine perfusion (perfusion group; n = 8) or injected intraarterially (manual group; n = 8) before replantation. Near-infrared fluorescence angiography was used to confirm thrombus formation and to assess tissue perfusion; muscle biopsy specimens were analyzed for ischemia/reperfusion injury directly after thrombolysis and 15 hours after replantation.

RESULTS

A higher incidence of secondary thrombosis was seen in the manual group compared to the perfusion group ( n = 6 versus n = 0, respectively; p < 0.001), resulting in two complete flap failures. Fifteen hours after replantation, mean fluorescence intensities were 13.0 (95 percent CI, 10.1 to 15.8) and 24.6 (95 percent CI, 22.0 to 27.2) in the perfusion and manual group, respectively ( p < 0.001), and mean muscle injury scores were comparable, measuring 7.5 ± 1.5.

CONCLUSION

Two hours of machine thrombolysis of compromised flaps in a porcine model showed higher salvage rates compared to a manual injection with tissue plasminogen activator and reduced the incidence of secondary thrombosis.

CLINICAL RELEVANCE STATEMENT

Using machine perfusion systems for ex vivo thrombolysis provides the benefits of local treatment of a composite tissue without the risk of systemic complications and may improve salvage rates and reduce the incidence of secondary thrombosis.

Ex Vivo Thrombolysis to Salvage Free Flaps Using Machine Perfusion: A Pilot Study in a Porcine Model

BACKGROUND

 Mechanical evacuation of capillary thrombi in free flaps is difficult, and often requires thrombolytic therapy. Utilizing machine perfusion systems, the possibility rises to salvage free flaps ex vivo by administering high doses of thrombolytic agents. The primary aim of this pilot study in a porcine model is to investigate the feasibility of ex vivo thrombolysis using an extracorporeal perfusion machine.

METHODS

 A model of stasis-induced thrombosis was used in 12 free rectus abdominis flaps harvested from six Dutch Landrace pigs. Compromised flaps were ex vivo perfused with University of Wisconsin preservation solution and treated according to the following study groups: (1) 1 mg of tissue plasminogen activator (t-PA) as additive, (2) 3 mg of t-PA as an additive, and (3) no thrombolytic additive. Microcirculation was assessed using near-infrared fluorescence angiography.

RESULTS

 Pedicled abdominal flaps were created and thrombus formation was successfully induced. Eleven abdominal flaps were perfused using the modified heart-lung machine setup. Near-infrared fluorescence angiography showed delayed or no filling was noted in the control group. In comparison, the flaps which were perfused with 1 mg t-PA or 3 mg t-PA as additive showed increased fluorescence intensity curves.

CONCLUSION

 This pilot study in a porcine model presents a reliable and reproductive stasis-induced thrombosis model in free flaps. By adding t-PA to a custom-made extracorporeal perfusion system, the indocyanine green fluorescence intensity curves increased of all flaps that were perfused with different dosages of t-PA as additives, indicating restoration of capillary pressure and microcirculatory inflow.

Anterograde Injection of Alteplase Salvages Deep Inferior Epigastric Perforator Flap in Reconstructive Breast Surgery

The DIEP flap is currently considered the gold standard for autologous reconstructive breast surgery. Postoperative flap failure due to microvascular postanastomotic thrombotic occlusion is a rare but severe complication. Alteplase, a thrombolytic agent typically used in the setting of an ischemic stroke, myocardial infarction, or pulmonary embolism, has also been injected into the microcirculation of flaps as a rescue procedure due to imminent flap loss. The purpose of this article is to provide an overview and detailed guidance for such a thrombolytic procedure due to suspected thrombotic microsurgical failure in free flap surgery. We report the case of a 43-year-old woman who underwent unilateral breast reconstruction with a DIEP flap at our department. Approximately 12 hours postoperatively, an arterial inflow problem was suspected and revision surgery was performed. Peripheral flap perfusion remained absent without an obvious cause and distal thrombosis was assumed to be present. Therefore, alteplase was gradually injected into the arterial pedicle in the anterograde direction just distal to the anastomosis while clamping the artery proximally. About 3 hours after selective flap thrombolysis, microcirculation of the flap was successfully restored without complications. Anterograde injection of alteplase can successfully salvage a free flap. To our knowledge, evidence for optimal dosing and delivery of alteplase for the treatment of thrombosed DIEP flaps has not been published to date. Our approach presents a therapeutic option that both maximizes alteplase concentration in the flap and minimizes the dosage required for flap salvage to significantly reduce systemic adverse effects.

Use of saline contrast ultrasonography in the diagnosis of complete jugular vein occlusion in a horse

Background

Thrombophlebitis and thrombosis are the most common causes of jugular vein occlusion in horses. Medical and surgical treatments aim to recanalize the occluded vessel and reduce proximal venous congestion and edema.

Case Description

The present report describes a clinical case of equine jugular vein thrombosis (JVT) with complete vein occlusion diagnosed by saline contrast ultrasonography (SCU) and confirmed by contrast venography.

Conclusion

Our results demonstrated that the SCU test can be easily performed and objectively interpreted using standard ultrasound equipment; it is not expensive and it does not require x-ray exposure. The SCU test is a valid tool to assess vessel patency and presence of collateral circulation in JVT. The test could therefore be used to monitor the progression of the disease and the effectiveness of therapy against JVT in horses.

High-level expression of a novel recombinant human plasminogen activator (rhPA) in the milk of transgenic rabbits and its thrombolytic bioactivity in vitro

The human tissue-type plasminogen activator (tPA) is a key kinase of fibrinolysis that plays an important role in dissolving fibrin clots to promote thrombolysis. The recombinant human plasminogen activator (rhPA) has more thrombolytic advantages than the wild type tPA. To increase the half-life and thrombolytic activity of tPA, a mutant containing only the essential K2 fibrin-binding and P activating plasminogen domains of the wild type tPA was cloned. This fragment was then inserted into goat β-casein regulatory sequences. Then, a mammary gland-specific expression vector, PCL25/rhPA, was constructed, and the transgenic rabbits were generated. In this study, 18 live transgenic founders (12♀, 6♂) were generated using pronuclear microinjection. Six transgenic rabbits were obtained, and the expression levels of rhPA in the milk had a range of 15.2-630 µg/ml. A fibrin agarose plate assay of rhPA showed that it had strong thrombolytic bioactivity in vitro, and the highest specific activity was >360 (360 times more than that of alteplase). The results indicated that the rhPA containing only the K2 and P domains is efficiently expressed with higher thrombolytic bioactivity in the milk of transgenic rabbits. Our study also demonstrated a new method for the large-scale production of clinically relevant recombinant pharmaceutical proteins in the mammary glands of transgenic rabbits.

Targeted thrombolysis strategies for neuroprotective effect

Stroke is usually treated by systemic thrombolytic therapy if the patient presents within an appropriate time window. There is also widespread interest in the development of thrombolytic agents that can be used in cases of delayed presentation. Current agents that can be used in cases of delayed presentation of nerve damage by thrombus. Current systemic thrombolytic therapy is associated with adverse effects such as fibrinogenolysis and bleeding. In an attempt to increase the efficacy, safety, and specificity of thrombolytic therapy, a number of targeted thrombolytic agents have been studied in recent years. This review focuses on the concepts underlying targeted thrombolytic therapy and describes recent drug developments in this field.