Effect of Thrombus Composition and Viscosity on Sonoreperfusion Efficacy in a Model of Micro-Vascular Obstruction

Long-pulsed ultrasound-mediated microbubble thrombolysis in a rat model of microvascular obstruction

In up to 30% patients who experience acute myocardial infarction, successful recanalization of the epicardial coronary artery cannot provide adequate microvascular reperfusion. In this study, we sought to determine whether long-pulsed ultrasound (US)-mediated microbubble (MB) cavitation was useful for the treatment of microvascular obstruction, and the therapeutic effects were compared within different long-pulse-length and short-pulsed US. Microvascular obstruction model was established by injecting micro-thrombi into common iliac artery of a rat's hind limb. About 1 MHz US with different long pulse lengths (ranging from 100 to 50,000 cycles) was delivered, compared to short pulse (5 cycles). The control group was given MB only without therapeutic US. Contrast perfusion images were performed at baseline, emboli, and 1, 5, 10 min post-embolization, and peak plateau video intensity (A) was obtained to evaluate the therapeutic effects. Long-tone-burst US showed better thrombolytic effects than short-pulsed US (1,000, 5,000 cycles >500 cycles, >5 cycles, and control) (P < 0.01). 1,000 cycles group showed the optimal thrombolytic effect, but microvascular hemorrhage was observed in 50,000 cycles group. In conclusion, long-tone-burst US-enhanced MB therapy mediated successful thrombolysis and may offer a powerful approach for the treatment for microvascular obstruction within a certain pulse length.

Mediation of long-pulsed ultrasound enhanced microbubble recombinant tissue plasminogen activator thrombolysis in a rat model of platelet-rich thrombus

Background

Ultrasound (US)-enhanced microbubble (MB) therapy has been investigated as a therapeutic technique to facilitate the thrombolysis for the treatment of pericardial and microvascular obstruction. This study sought to assess the therapeutic effects of long-pulsed US-assisted MB-mediated recombinant tissue plasminogen activator (rt-PA) thrombolysis in a rat model of platelet-rich thrombus.

Methods

Ferric chloride (10%) was used to induce total arterial occlusion before formation of platelet-rich thrombi. Therapeutic long-tone-burst US (1 MHz, 0.6 MPa, 1,000-µs pulse length) was used, and 2.9×109/mL of lipid MBs and 1 mg/mL of rt-PA were infused. Subsequently, 42 Sprague-Dawley (SD) male rats were randomly divided into seven groups: (I) control; (II) rt-PA; (III) high duty cycle US + MB; (IV) low duty cycle US + rt-PA; (V) high duty cycle US + rt-PA; (VI) low duty cycle US + rt-PA + MB; and (VII) high duty cycle US + rt-PA + MB. The recanalization grades were evaluated after 20 minutes' treatment.

Results

Compared to the control, there was significant improvement in recanalization in the US + rt-PA groups (P=0.01 vs. control), US (low duty cycle) + rt-PA + MB (P=0.003 vs. control) and US (high duty cycle) + rt-PA + MB (P<0.001 vs. control) groups, in which recanalization was successfully achieved in all rats.

Conclusions

Long-pulsed US-enhanced MB-mediated rt-PA thrombolysis offered a powerful approach in the treatment of platelet-rich thrombus.

Dynamic Behavior of Polymer Microbubbles During Long Ultrasound Tone-Burst Excitation and Its Application for Sonoreperfusion Therapy

OBJECTIVE

Ultrasound (US)-targeted microbubble (MB) cavitation (UTMC)-mediated therapies have been found to restore perfusion and enhance drug/gene delivery. Because of the potentially longer circulation time and relative ease of storage and reconstitution of polymer-shelled MBs compared with lipid MBs, we investigated the dynamic behavior of polymer microbubbles and their therapeutic potential for sonoreperfusion (SRP) therapy.

METHODS

The fate of polymer MBs during a single long tone-burst exposure (1 MHz, 5 ms) at various acoustic pressures and MB concentrations was recorded via high-speed microscopy and passive cavitation detection (PCD). SRP efficacy of the polymer MBs was investigated in an in vitro flow system and compared with that of lipid MBs.

DISCUSSION

Microscopy videos indicated that polymer MBs formed gas-filled clusters that continued to oscillate, fragment and form new gas-filled clusters during the single US burst. PCD confirmed continued acoustic activity throughout the 5-ms US excitation. SRP efficacy with polymer MBs increased with pulse duration and acoustic pressure similarly to that with lipid MBs but no significant differences were found between polymer and lipid MBs.

CONCLUSION

These data suggest that persistent cavitation activity from polymer MBs during long tone-burst US excitation confers excellent reperfusion efficacy.

Effect of Ultrasound Pulse Length on Sonoreperfusion Therapy

In recent years, long- and short-pulse ultrasound (US)-targeted microbubble cavitation (UTMC) has been found to increase perfusion in healthy and ischemic skeletal muscle, in pre-clinical animal models of microvascular obstruction and in the myocardium of patients presenting with acute myocardial infarction. There is evidence that the observed microvascular vasodilation is driven by the nitric oxide pathway and purinergic signaling, but the time course of the response and the dependency on US pulse length are not well elucidated. Because our prior data supported that sonoreperfusion efficacy is enhanced by long-pulse US versus short-pulse US, in this study, we sought to compare long-pulse (5000 cycles) and short-pulse (500 × 10 cycles) US at a pressure of 1.5 MPa with an equivalent total number of acoustical cycles, hence constant acoustic energy, and at the same frequency (1 MHz), in a rodent hind limb model with and without microvascular obstruction (MVO). In quantifying perfusion using burst replenishment contrast-enhanced US imaging, we made three findings: (i) Long and short pulses result in different vasodilation kinetics in an intact hind limb model. The long pulse causes an initial spasmic reduction in flow that spontaneously resolved at 4 min, followed by sustained higher flow rates (approximately twofold) compared with baseline, starting 10 min after therapy (p < 0.05). The short pulse caused a short-lived approximately twofold increase in flow rate that peaked at 4 min (p < 0.05), but without the initial spasm. (ii) The sustained increased response with the long pulse is not simply reactive hyperemia. (iii) Both pulses are effective in reperfusion of MVO in our hindlimb model by restoring blood volume, but only the long pulse caused an increase in flow rate after treatment ii, compared with MVO (p < 0.05). Histological analysis of hind limb muscle post-UTMC with either pulse configuration indicates no evidence of tissue damage or hemorrhage. Our findings indicate that the microbubble oscillation induces vasodilation, and therapeutic efficacy for the treatment of MVO can be tuned by varying pulse length; relative to short-pulse US, longer pulses drive greater microbubble cavitation and more rapid microvascular flow rate restoration after MVO, warranting further optimization of the pulse length for sonoreperfusion therapy.

Effect of Gambogic Acid-Loaded Porous-Lipid/PLGA Microbubbles in Combination With Ultrasound-Triggered Microbubble Destruction on Human Glioma

Gambogic acid (GA) is a highly effective antitumor agent, and it is used for the treatment of a wide range of cancers. It is challenging to deliver drugs to the central nervous system due to the inability of GA to cross the blood-brain barrier (BBB). Studies have shown that ultrasound-targeted microbubble destruction can be used for transient and reversible BBB disruption, significantly facilitating intracerebral drug delivery. We first prepared GA-loaded porous-lipid microbubbles (GA porous-lipid/PLGA MBs), and an in vitro BBB model was established. The cell viability was detected by CCK-8 assay and flow cytometry. The results indicate that U251 human glioma cells were killed by focused ultrasound (FUS) combined with GA/PLGA microbubbles. FUS combined with GA/PLGA microbubbles was capable of locally and transiently enhancing the permeability of BBB under certain conditions. This conformational change allows the release of GA to extracellular space. This study provides novel targets for the treatment of glioma.

Myocardial blush grade: a determinant of left ventricular ejection fraction and adverse outcomes in STEMI

BACKGROUND AND AIMS

Despite restoration of blood flow, subtle microvascular obstruction can occur. This obstruction can be graded using myocardial blush grade. We aimed to investigate the role of myocardial blush grade in ejection fraction and adverse outcomes, after percutaneous intervention.

METHODS

A prospective, observational study was conducted at our institute with a calculated sample size. Variables such as age, gender, and ejection fraction were noted before the intervention. The patients were followed for 3 months to determine the outcomes. The data was analyzed using IBM SPSS software version 26.0. P-value of less than 0.05 was considered significant for the statistical tests.

RESULTS

There were 74 male and 36 female participants in the study. The mean age was 52.20 ± 10.02 years. The most common adverse outcome was heart failure (18%). There was a significant Pearson's correlation between myocardial blush grade and improvement in ejection fraction (p < 0.05). Improvement in myocardial blush grade was significantly related to a decrease in adverse outcomes (p < 0.05). Regression analysis proved myocardial blush grade and diabetes status as independent predictors of percentage increase in ejection fraction (p < 0.05).

CONCLUSION

High myocardial blush grade is one of the independent predictors of better outcomes in ST-elevation myocardial infarction.

Sonoreperfusion therapy for microvascular obstruction: A step toward clinical translation

Sonoreperfusion therapy is being developed as an intervention for the treatment of microvascular obstruction. We investigated the reperfusion efficacy of two clinical ultrasound systems (a modified Philips EPIQ and a Philips Sonos 7500) in a rat hindlimb microvascular obstruction model. Four ultrasound conditions were tested using 20 min treatments: Sonos single frame, Sonos multi-frame, EPIQ low pressure and EPIQ high pressure. Contrast-enhanced perfusion imaging of the microvasculature was conducted at baseline and after treatment to calculate microvascular blood volume (MBV). EPIQ high pressure treatment resulted in significant recovery of MBV from microvascular obstruction, returning to baseline levels after treatment. EPIQ low pressure and Sonos multi-frame treatment resulted in significantly improved MBV after treatment but below baseline levels. Sonos single-frame and control groups showed no improvement post-treatment. This study demonstrates that the most effective sonoreperfusion therapy occurs at high acoustic pressure coupled with high acoustic intensity. Moreover, a clinically available ultrasound system is readily capable of delivering these effective therapeutic pulses.

Sonobactericide: An Emerging Treatment Strategy for Bacterial Infections

Ultrasound has been developed as both a diagnostic tool and a potent promoter of beneficial bio-effects for the treatment of chronic bacterial infections. Bacterial infections, especially those involving biofilm on implants, indwelling catheters and heart valves, affect millions of people each year, and many deaths occur as a consequence. Exposure of microbubbles or droplets to ultrasound can directly affect bacteria and enhance the efficacy of antibiotics or other therapeutics, which we have termed sonobactericide. This review summarizes investigations that have provided evidence for ultrasound-activated microbubble or droplet treatment of bacteria and biofilm. In particular, we review the types of bacteria and therapeutics used for treatment and the in vitro and pre-clinical experimental setups employed in sonobactericide research. Mechanisms for ultrasound enhancement of sonobactericide, with a special emphasis on acoustic cavitation and radiation force, are reviewed, and the potential for clinical translation is discussed.

Intra-clot Microbubble-Enhanced Ultrasound Accelerates Catheter-Directed Thrombolysis for Deep Vein Thrombosis: A Clinical Study

Insufficiency of microbubbles in the vessel-obstructing thrombus significantly reduces the effectiveness of ultrasound thrombolysis. With catheter-directed thrombolysis (CDT), microbubbles can be delivered directly into the thrombus. In this study, we combined CDT with intra-clot microbubble-enhanced ultrasound thrombolysis (IMUT) to investigate its safety and efficiency in thrombolysis in patients with acute lower limb deep vein thrombosis (DVT). For IMUT, a 1-MHz air-backed transducer directed 100-μs-pulse-length and 100-Hz-pulse-repetition pressure at 1 MPa was used. Thirteen DVT patients in the study group were treated with CDT and IMUT. Forty-three DVT patients in the historical control group were treated with CDT alone. The results indicated that the average thrombolysis time of the study group was significantly shorter (5.23 ± 1.59 d) than that of the control (10.00 ± 2.69 d), and the overall urokinase dosage of the study group ([3.82 ± 1.68] × 10⁶ IU) was lower than that of the control ([4.99 ± 2.26] × 10⁶ IU). No procedure-related complications were noted in either group. Therefore, combining CDT with IMUT can improve thrombolysis safely and efficiently.

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

We have previously reported that long-tone-burst, high-mechanical-index ultrasound (US) and microbubble (MB) therapy can restore perfusion in both in vitro and in vivo models of microvascular obstruction (MVO). Addition of MBs to US has been found 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 cycle, 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 compared with 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 employed 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.

Sonoreperfusion Therapy Kinetics in Whole Blood Using Ultrasound, Microbubbles and Tissue Plasminogen Activator

Coronary intervention for myocardial infarction often results in microvascular embolization of thrombus. Sonoreperfusion therapy (SRP) using ultrasound and microbubbles restored perfusion in our in vitro flow model of microvascular obstruction. In this study, we assessed SRP efficacy using whole blood as the perfusate with and without tissue plasminogen activator (tPA). In a phantom vessel bearing a 40-μm-pore mesh to simulate the microvasculature, microthrombi were injected to cause microvascular obstruction and were treated using SRP. Without tPA, the lytic rate increased from 2.6 ± 1.5 mmHg/min with 1000-cycle pulses to 7.3 ± 3.2 mmHg/min with 5000-cycle ultrasound pulses (p < 0.01). The lytic index was similar for tPA-only ([2.0 ± 0.5] × 10^-3 mmHg^-1 min^-1) and 5000 cycles without tPA ([2.3 ± 0.5] × 10^-3 mmHg^-1 min^-1) (p = 0.5) but increased ([3.6 ± 0.8] × 10^-3 mmHg^-1 min^-1) with tPA in conjunction with 5000-cycles ultrasound (p < 0.01). In conclusion, SRP restored microvascular perfusion in whole blood, SRP lytic rate in experiments without tPA increased with ultrasound pulse length and efficacy increased with the addition of tPA.