Inertial Cavitation Ultrasound with Microbubbles Improves Reperfusion Efficacy When Combined with Tissue Plasminogen Activator in an In Vitro Model of Microvascular Obstruction

Abstract

We have previously shown that long tone burst high mechanical index ultrasound (US) and microbubble (MB) therapy can restore perfusion in both an in vitro and in vivo model of microvascular obstruction (MVO). Addition of MB to US has been shown to potentiate the efficacy of thrombolytics on large venous thrombi, however the optimal US parameters for achieving microvascular reperfusion of MVO caused by microthrombi, when combined with tissue plasminogen activator (tPA) are unknown. We sought to elucidate the specific effects of US, with and without tPA, for effective reperfusion of MVO in an in vitro model using both venous and arterial microthrombi. Venous and arterial type microthrombi were infused onto a mesh with 40-μm pores to simulate MVO. Pulsed US (1 MHz) was delivered with inertial cavitation (IC) (1.0 MPa, 1000 cycles, 0.33 Hz) and stable cavitation (SC) US (0.23 MPa, 20% duty, 0.33 Hz) regimes while MB suspension (2×106 MBs/mL) was infused. The efficacy of sonoreperfusion with these parameters was tested with and without tPA. Sonoreperfusion efficacy was significantly greater for IC+tPA when compared to tPA alone, IC, SC, and SC+tPA, suggesting lytic synergism between tPA and US for both venous and arterial type microthrombi. In contrast to our previous in vitro studies using 1.5 MPa at 5000 US cycles without tPA, the IC regime used herein used 90% less US energy. These findings suggest an IC regime can be used with tPA synergistically to achieve a high degree of fibrinolysis for both thrombus types.

Diagnostic Ultrasound and Microbubbles Treatment Improves Outcomes of Coronary No-Reflow in Canine Models by Sonothrombolysis

“…More importantly, US+MB treatment decreased the percentage of microthrombi-occluded myocardial arterioles, as indicated by systemic histologic analysis of postmortem myocardium. These findings indicated that MB-mediated sonothrombolysis could efficiently dissolve coronary microthrombi, which is partially supported by previous in vivo and in vitro studies ( 20 – 22 , 29 ). Additionally, it is widely accepted that the burden of thrombotic microemboli is highly predictive of the occurrence of CnRF ( 30 ), and timely restoration of MBF by eliminating these emboli is the cornerstone of alleviating myocardial injury and preserving cardiac functions.…”

Ultrasound-Responsive Cavitation Nuclei for Therapy and Drug Delivery

“…Petit et al (2015) observed a greater degree of rt-PA lysis with BR38 microbubbles exposed to 1 MHz pulsed ultrasound at an amplitude causing inertial cavitation (1.3 MPa peak rarefactional pressure) than at a lower amplitude causing stable cavitation (0.35 MPa peak rarefactional pressure). Goyal et al (2017) also measured a higher degree of thrombolysis with 1 MHz pulsed ultrasound at 1.0 MPa peak rarefactional pressure with inertial cavitation than at 0.23 MPa peak rarefactional pressure with stable cavitation in an in vitro model of microvascular obstruction using perfluorobutane-filled, lipid-shelled microbubbles (Weller et al 2002) as a nucleation agent. However, Kleven et al (2019) observed more than 60% fractional clot width loss for highly retracted human whole blood clots exposed to rt-PA, Definity and 220 kHz pulsed or continuous wave (CW) ultrasound at an acoustic output with sustained stable cavitation throughout the insonification periods (0.22 MPa peak rarefactional pressure) (Fig.…”

“…While fluorinated gases improve the stability of phospholipid-coated microbubbles (Rossi et al 2011), other gases can be loaded for therapeutic applications, such as oxygen for treatment of tumors (McEwan et al 2015;Fix et al 2018;Nesbitt et al 2018) and nitric oxide (Kim et al 2014;Sutton et al 2014) and hydrogen gas (He et al 2017) for treatment of cardiovascular disease. The main phospholipid component of custom-made microbubbles is usually a phosphatidylcholine such as 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), used in 13 studies (e.g., Dewitte et al 2015;Bae et al 2016;Chen et al 2016;Fu et al 2019), or 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), used in 18 studies (e.g., Kilroy et al 2014;Bioley et al 2015;Dong et al 2017;Goyal et al 2017;Pandit et al 2019). These phospholipids are popular because they are also the main components in Definity (Definity 2011) and SonoVue/Lumason (Lumason 2016), respectively.…”

In vitro characterization of sonothrombolysis and echocontrast agents to treat ischemic stroke

“…Ultrasound (US) exposure of echocontrast agents has been investigated as an adjuvant to enhance rt-PA thrombolysis in previous in vitro 22–26 , ex vivo 27 , and in vivo studies 28–30 . Our group has reported enhanced thrombolysis in the presence of 120-kHz US with echogenic liposomes 31 .…”