Pulsed High-Intensity Focused Ultrasound Enhances Thrombolysis in an in Vitro Model

Abstract

Purpose-To evaluate the use of pulsed high-intensity focused ultrasound exposures to improve tissue plasminogen activator (tPA)-mediated thrombolysis in an in vitro model. Materials and Methods-All experimental work was compliant with institutional guidelines andHIPAA. Clots were formed by placing 1 mL of human blood in closed-off sections of pediatric Penrose tubes. Four experimental groups were evaluated: control (nontreated) clots, clots treated with pulsed high-intensity focused ultrasound only, clots treated with tPA only, and clots treated with pulsed high-intensity focused ultrasound plus tPA. The focused ultrasound exposures (real or sham) were followed by incubations of the clots in tPA with saline or in saline only. Thrombolysis was measured as the relative reduction in the mass of the clot. D-Dimer assays also were performed. Two additional experiments were performed and yielded dose-response curves for two exposure parameters: number of pulses per raster point and total acoustic power. Radiation force-induced displacements caused by focused ultrasound exposures were simulated in the clots. A Tukey-Kramer honestly significant difference test was performed for comparisons between all pairs of experimental groups.Results-The clots treated with focused ultrasound alone did not show significant increases in thrombolysis compared with the control clots. The clots treated with focused ultrasound plus tPA showed a 50% ([30.2/20.1]/20.1) increase in the degree of thrombolysis compared with the clots treated with tPA only (P < .001), further corroborating the D-dimer assay results (P < .001). Additional experiments revealed how increasing both the number of pulses per raster point and the total acoustic power yielded corresponding increases in the thrombolysis rate. In the latter experiment, simulations performed at a range of power settings revealed a direct correlation between increased displacement and observed thrombolysis rate.Conclusion-The rate of tPA-mediated thrombolysis can be enhanced by using pulsed highintensity focused ultrasound exposure in vitro.Venous thromboembolism, which includes deep venous thrombosis and pulmonary embolism, accounts for about 250 000 hospitalizations per year in the United States (1). Venous Address correspondence to V.F. (e-mail: vfrenkel@cc.nih.gov For decades patients with venous thrombosis have been treated primarily with anticoagulation, which is usually effective at slowing further thrombus formation. However, anticoagulation is often inadequate for eliminating the source of subsequent emboli, alleviating the hemodynamic disturbances, preventing subsequent valvular damage, and preventing permanent impairment to the pulmonary vascular bed (3). For this reason, more aggressive therapy, such as thrombolysis or thrombectomy, is sometimes used.Ultrasound has been studied as a treatment adjunct to thrombolytic drugs for thrombolysis, as well as an independent treatment method in various models (4-9). Catheter-based systems have been used with oscillating wires to ...

Pulsed-high intensity focused ultrasound enhanced tPA mediated thrombolysis in a novel in vivo clot model, a pilot study

“…Using fluorescently labeled antibodies to tPA, we showed how these nondestructive changes enabled improved penetration and binding of the drug, both at the clots' surface and within its interior [18]. This mechanism would seem to explain the enhancing effect of pulsed-HIFU on tPA-mediated thrombolysis observed in our in vitro [17] study, and similarly could explain the results in the present study. These results are supported by additional studies in purified fibrin gels, where ultrasound exposures caused reversible fiber disaggregation [23], and consequently improved fluid flow through the gels [24].…”

“…Pulsed-HIFU has previously been used to enhance the delivery of various substances in animal tumor models, including chemotherapeutic agents, nanoparticles, and plasmid DNA [13], and was shown to increase tPA-mediated thrombolysis in vitro [17]. In this study we demonstrated that pulsed-HIFU can also significantly enhance tPA-mediated thrombolysis in a novel in vivo model.…”

“…Pulsed-HIFU also demonstrated the ability to enhance tissue plasminogen activator (tPA)-mediated thrombolysis in vitro. The lack of effects, without drug, and elevated D-dimer levels with pulsed-HIFU and drug compared to drug alone, suggest that increased thrombolysis was due to improved activity of tPA into the clots, and not mechanical degradation [17]. This hypothesis is supported by our recent study showing that pulsed-HIFU produced non-destructive, macroscopic alterations in clots that increased their exposed surface area, and consequently improved binding and penetration of the tPA (18).…”

“…This hypothesis is supported by our recent study showing that pulsed-HIFU produced non-destructive, macroscopic alterations in clots that increased their exposed surface area, and consequently improved binding and penetration of the tPA (18). These studies [17,18] were the basis of the current study, which evaluated the potential of using pulsed-HIFU to enhance tPA-mediated thrombolysis non-invasively in vivo. A novel clot model in the marginal ear vein of rabbits was developed specifically for this pilot study.…”

Reversible and irreversible vascular bioeffects induced by ultrasound and microbubbles in chorioallantoic membrane model

“…Similar transient vascular damage has previously been reported for blood brain barrier vasculature resulting in erythrocyte extravasation (15)(16)(17). Acoustic research is currently in progress to use USMB for thrombolysis (18,19) however the results from this study indicate that USMB may also cause temporary thrombus formation.…”