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: 2.43). 02/2008; 121(5):663-73. DOI: 10.1016/j.thromres.2007.07.006
Source: PubMed

ABSTRACT 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.

Download full-text


Available from: Christy K Holland, Aug 22, 2015
  • Source
    • "Thrombolysis ability of the uPA-loaded nanogels The thrombolysis capacity of uPA formulations is one of the most important characteristics that are closely related to the clinical applications (Holland et al., 2007; Hölscher et al., 2009). As shown in Fig. 5, it is found in the in vitro tests that the thrombolysis of uPA-loaded nanogels in silent condition is much lower than that of the nude uPA. "
    [Show abstract] [Hide abstract]
    ABSTRACT: To find a way to modulate the effect of thrombolytic proteins by increasing their specificity, minimizing their adverse effect as well as lengthening their circulation time for the treatment of ischemic vascular disease holds great promise. In this work, urokinase-type plasminogen activator (uPA) was encapsulated into hollow nanogels which are generated by the reaction of glycol chitosan and aldehyde capped poly(ethylene glycol) (OHC-PEG-CHO) through a one-step approach of ultrasonic spray. The uPA-loaded nanogels, with size of 200-300 nm, have longer circulation time than that of the nude urokinase in vivo, besides the protein can be triggered to release in faster rate under diagnostic ultrasonic condition of 2 MHz, which significantly enhanced the thrombolysis of clots. The results are promising for increasing the specificity and positive effects of thrombolytic agents like recombinant tissue plasminogen activator (rt-PA) for the current treatment of ischemic vascular disease.
    International Journal of Pharmaceutics 06/2012; 434(1-2):384-90. DOI:10.1016/j.ijpharm.2012.06.001 · 3.65 Impact Factor
  • Source
    • "The power field was estimated using the KZK model [20]. The temperature vs time history was obtained by solving the bio-heat equation proposed by Pennes numerically [22]. The explicit form of this equation is given by: "
    [Show abstract] [Hide abstract]
    ABSTRACT: Introduction: in this paper a simulation model for predicting the temperature during the application of focused ultrasound (FUS) for stroke treatment using pulsed ultrasound is presented. Materials and meth-ods: a single element spherically focused transducer of 5 cm diameter, focusing at 10 cm and operating at either 0.5 MHz or 1 MHz was considered. The power field was estimated using the Khokhlov-Zabolot-skaya-Kuznetzov (KZK) model. The temperature was estimated using the bioheat equation. The goal was to extract the acoustic parameters (frequency, power, and duty factor) that maintain a temperature increase of less than 1˚C during the application of a pulse ultrasound protocol. Results: it was found that the temperature change increases linearly with duty factor. The higher the power, the lower the duty fac-tor needed to keep the temperature change to the safe limit of 1˚C. The higher the frequency the lower the duty factor needed to keep the temperature change to the safe limit of 1˚C. Finally, the shallow the target, the lower the duty factor needed to keep the tem-perature change to the safe limit of 1˚C. The simula-tion model was tested in brain tissue during the ap-plication of pulse ultrasound and the measured tem-perature was in close agreement with the simulated temperature. Conclusions: This simulation model is considered to be very useful tool for providing acous-tic parameters (frequency, power, and duty factor) during the application of pulsed ultrasound at vari-ous depths in tissue so that a safe temperature is maintained during the treatment. This model will be tested eventually during stroke clinical trials.
    Journal of biomedical science and engineering 01/2011; 445052(05):410-417. DOI:10.4236/jbise.2011.45052 · 0.27 Impact Factor
  • Source
    • "Of course, acoustic streaming can occur in blood due to the absorption of sound [4], but it is difficult to obtain significant streaming with a Doppler waveform alone. On the other hand, if microbubbles are present, then streaming can be greatly enhanced [5] due to the strong radiation forces exerted by ultrasound on bubbles, as well as microstreaming induced by the pulsations of the bubbles themselves; thus, there is significant research activity in the combined use of ultrasound contrast agents (stabilized microbubbles) together with pulsed ultrasound, with and without a thrombolytic drug. It is likely that when ultrasound is combined with t-PA alone (no ultrasound contrast agents), there are sufficient cavitation nuclei in the host fluid itself to induce some level of radiation-force type streaming. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Before ultrasound-imaging systems became widely available, ultrasound therapy devices showed great promise for general use in medicine. However, it is only in the last decade that ultrasound therapy has begun to obtain clinical acceptance. Recently, a variety of novel applications of therapeutic ultrasound have been developed that include sonothrombolysis, site-specific and ultrasound-mediated drug delivery, shock wave therapy, lithotripsy, tumor ablation, acoustic hemostasis and several others. This paper reviews a few selected applications of therapeutic ultrasound. It will address some of the basic scientific questions and future challenges in developing these methods and technologies for general use in our society. As a plenary presentation, its audience is intended for the ultrasound scientist or engineer, and thus is not presented at the level of the experienced medical ultrasound professional.
    Physics Procedia 01/2010; 3(1):25-34. DOI:10.1016/j.phpro.2010.01.005
Show more