Ultrasound-enhanced tissue plasminogen activator thrombolysis in an in vitro porcine clot model

Department of Biomedical Engineering, University of Cincinnati, Medical Science Building, Rm. 6167, 231 Albert Sabin Way, Cincinnati, OH 45267-0586, USA.
Thrombosis Research (Impact Factor: 2.45). 02/2008; 121(5):663-73. DOI: 10.1016/j.thromres.2007.07.006
Source: PubMed


Thrombolytics such as recombinant tissue plasminogen activator (rt-PA) have advanced the treatment of ischemic stroke, myocardial infarction, deep vein thrombosis and pulmonary embolism.
To improve the efficacy of this thrombolytic therapy, the synergistic effect of rt-PA and 120 kHz or 1.0 MHz ultrasound was assessed in vitro using a porcine clot model.
Fully retracted whole blood clots prepared from fresh porcine blood were employed to compare rt-PA thrombolytic treatment with and without exposure to 120-kHz or 1-MHz ultrasound. For sham studies (without ultrasound), clot mass loss was measured as a function of rt-PA concentration from 0.003 to 0.107 mg/ml. For combined ultrasound and rt-PA treatments, peak-to-peak pressure amplitudes of 0.35, 0.70 or 1.0 MPa were employed. The range of duty cycles varied from 10% to 100% (continuous wave) and the pulse repetition frequency was fixed at 1.7 KHz.
For rt-PA alone, the mass loss increased monotonically as a function of rt-PA concentration up to approximately 0.050 mg/ml. With ultrasound and rt-PA exposure, clot mass loss increased by as much as 104% over rt-PA alone. Ultrasound without the presence of rt-PA did not significantly enhance thrombolysis compared to control treatment. The ultrasound-mediated clot mass loss enhancement increased with the square root of the overall treatment duration.
Both 120-kHz and 1-MHz pulsed and CW ultrasound enhanced rt-PA thrombolysis in a porcine whole blood clot model in vitro. No clear dependence of the observed thrombolytic enhancement on ultrasound duty cycle was evident. The lack of duty cycle dependence suggests a more complex mechanism that could not be sustained by merely increasing the pulse duration.

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Available from: Christy K Holland
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    • "This is because clinical therapies and thrombolytic agents' responses to thrombolysis depend on the thrombus age [3] [4]. Aged thrombi are more resistant to thrombolysis than fresh thrombi [5] [6] [7] [8]. Thrombi appearance may predict the efficacy of thrombolysis [9]. "
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    • "The mix was poured into a 100 mL Petri dish (⌀100 mm × 12 mm), which was incubated at 37°C for 5 min⁡ during coagulation process. Once coagulated, the blood was preserved at 4°C in the closed Petri dish during three days in order to ensure clot retraction [28–31]. It was then used for the experiments within three days. "
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    • "Recently, ultrasound-assisted drug delivery has been investigated as a method of targeting a specific area (Klibanov et al., 2010), and intrinsically echogenic liposomes have been used as a vehicle to achieve ultrasound-triggered controlled drug release (Huang, 2008; Greineder et al., 2013). Ultrasound was found to improve the effectiveness of tissue plasminogen activator (tPA), but was associated with hemorrhagic side effects (Datta et al., 2006; Holland et al., 2008; Meunier et al., 2009). Use of tPA-loaded intrinsically echogenic liposomes was found to be similarly effective to other treatment methods, while offering the advantages of ultrasound monitoring and enhanced thrombolysis with site-specific delivery (Shaw et al., 2009; Laing et al., 2012). "
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