Combined Low-Frequency Ultrasound and Urokinase-Containing Microbubbles in Treatment of Femoral Artery Thrombosis in a Rabbit Model

Contrast enhanced sonothrombolysis using streptokinase loaded phase change nano-droplets for potential treatment of deep venous thrombosis

Current thrombolytic therapies for deep venous thrombosis are limited due to the wide side effect profile. Contrast mediated sonothrombolysis is a promising approach for thrombus treatment. The current study examines the effectiveness of in vitro streptokinase (SK) loaded phase-change nanodroplet (PCND) mediated sonothrombolysis at 7 MHz for the diagnosis of deep venous thrombosis. Lecithin shell and perfluorohexane core nanodroplets were prepared via the thin-film hydration method and morphologically characterized. Sonothrombolysis was performed at 7 MHz at different mechanical indexes of samples i.e., only sonothrombolysis, PCND mediated sonothrombolysis, sonothrombolysis with SK and SK loaded PCND mediated sonothrombolysis. Thrombolysis efficacy was assessed by measuring clot weight changes during 30 min US exposure, recording the mean gray intensity from the US images of the clot by computer software ImageJ, and spectrophotometric quantification of the hemoglobin in the clot lysate. In 15 minutes of sonothrombolysis performed at high mechanical index (0.9 and 1.2), SK loaded PCNDs showed a 48.61% and 74.29% reduction of mean gray intensity. At 0.9 and 1.2 MI, 86% and 92% weight loss was noted for SK-loaded PCNDs in confidence with spectrophotometric results. A significant difference (P < 0.05) was noted for SK-loaded PCND mediated sonothrombolysis compared to other groups. Loading of SK inside the PCNDs enhanced the efficacy of sonothrombolysis. An increase in MI and time also increased the efficacy of sonothrombolysis. This in vitro study showed the potential use of SK-loaded perfluorohexane core PCNDs as sonothrombolytic agents for deep venous thrombosis.

Contrast enhanced sonothrombolysis using streptokinase loaded phase change nano-droplets.

Therapeutic Use of Microbubbles and Ultrasound in Acute Peripheral Arterial Thrombosis: A Systematic Review

Catheter-directed thrombolysis (CDT) for acute peripheral arterial occlusion is time consuming and carries a risk of major hemorrhage. Contrast-enhanced sonothrombolysis (CEST) might enhance outcomes compared with standard CDT. In the study described here, we systematically reviewed all in vivo studies on contrast-enhanced sonothrombolysis in a setting of arterial thrombosis. A systematic search of the PubMed, Embase, Cochrane Library and Web of Science databases was conducted. Two reviewers independently performed the study selection, quality assessment and data extraction. Primary outcomes were recanalization rate and thrombus weight. Secondary outcome was any possible adverse event. The 35 studies included in this review were conducted in four different (pre)clinical settings: ischemic stroke, myocardial infarction, (peripheral) arterial thrombosis and arteriovenous graft occlusion. Because of the high heterogeneity among the studies, it was not possible to conduct a meta-analysis. In almost all studies, recanalization rates were higher in the group that underwent a form of CEST. One study was terminated early because of a higher incidence of intracranial hemorrhage. Studies on CEST suggest that adding microbubbles and ultrasound to standard intra-arterial CDT is safe and might improve outcomes in acute peripheral arterial thrombosis. Further research is needed before CEST can be implemented in daily practice.

Development and application of ultrasound contrast agents in biomedicine

With the rapid development of molecular imaging, ultrasound (US) medicine has evolved from traditional imaging diagnosis to integrated diagnosis and treatment at the molecular level. Ultrasound contrast agents (UCAs) play a crucial role in the integration of US diagnosis and treatment. As the micro-bubbles (MBs) in UCAs can enhance the cavitation effect and promote the biological effect of US, UCAs have also been studied in the fields of US thrombolysis, mediated gene transfer, drug delivery, and high intensity focused US. The application range of UCAs is expanding, and the value of their applications is improving. This paper reviews the development and application of UCAs in biomedicine in recent years, and the existing problems and prospects are pointed out.

A thrombolytic therapy using diagnostic ultrasound combined with RGDS-targeted microbubbles and urokinase in a rabbit model

This study aimed to explore thrombolysis therapy based on ultrasound combined with urokinase and Arg–Gly–Asp sequence (RGDS)-targeted microbubbles by evaluating the histological changes in a thrombotic rabbit model. Forty-two New Zealand rabbits featuring platelet-rich thrombi in the femoral artery were randomized to (n = 6/group): ultrasound alone (US); urokinase alone (UK); ultrasound plus non-targeted microbubbles (US + M); ultrasound plus RGDS-targeted microbubbles (US + R); RGDS-targeted microbubbles plus urokinase (R + UK); ultrasound, non-targeted microbubbles and urokinase (US + M + UK); and ultrasound, RGDS-targeted microbubbles and urokinase (US + R + UK) groups. Diagnostic ultrasound was used transcutaneously over the thrombus for 30 min. We evaluated the thrombolytic effect based on ultrasound thrombi detection, blood flow, and histological observations. Among all study groups, complete recanalization was achieved in the US + R + UK group. Hematoxylin and eosin staining showed that the thrombi were completely dissolved. Scanning electron microscopy examination demonstrated that the fiber network structure of the thrombi was damaged. Transmission electron microscopy showed that the thrombus was decomposed into high electron-dense particles. Histology for von Willebrand factor and tissue factor were both negative in the US + R + UK group. This study revealed that a thrombolytic therapy consisting of diagnostic ultrasound together with RGDS-targeted and urokinase coupled microbubbles.

Advances in Sonothrombolysis Techniques Using Piezoelectric Transducers

One of the great advancements in the applications of piezoelectric materials is the application for therapeutic medical ultrasound for sonothrombolysis. Sonothrombolysis is a promising ultrasound based technique to treat blood clots compared to conventional thrombolytic treatments or mechanical thrombectomy. Recent clinical trials using transcranial Doppler ultrasound, microbubble mediated sonothrombolysis, and catheter directed sonothrombolysis have shown promise. However, these conventional sonothrombolysis techniques still pose clinical safety limitations, preventing their application for standard of care. Recent advances in sonothrombolysis techniques including targeted and drug loaded microbubbles, phase change nanodroplets, high intensity focused ultrasound, histotripsy, and improved intravascular transducers, address some of the limitations of conventional sonothrombolysis treatments. Here, we review the strengths and limitations of these latest pre-clincial advancements for sonothrombolysis and their potential to improve clinical blood clot treatments.

Drug-Loaded Microbubbles Combined with Ultrasound for Thrombolysis and Malignant Tumor Therapy

Cardiac-cerebral thrombosis and malignant tumor endanger the safety of human life seriously. Traditional chemotherapy drugs have side effects which restrict their applications. Drug-loaded microbubbles can be destroyed by ultrasound irradiation at the focus position and be used for thrombolysis and tumor therapy. Compared with traditional drug treatment, the drug-loaded microbubbles can be excited by ultrasound and release drugs to lesion sites, increasing the local drug concentration and the exposure dose to nonfocal regions, thus reducing the cytotoxicity and side effects of drugs. This article reviews the applications of drug-loaded microbubbles combined with ultrasound for thrombolysis and tumor therapy. We focus on highlighting the advantages of using this new technique for disease treatment and concluding with recommendations for future efforts on the applications of this technology.

The Optimized Fabrication of a Novel Nanobubble for Tumor Imaging

Nanobubbles with a size of less than 1 µm can be used as ultrasound contrast agents for diagnosis and as drug/gene carriers for therapy. However, the optimal method of preparing uniform-sized nanobubbles is considered controversial. In this study, we developed novel biocompatible nanobubbles by performing differential centrifugation to isolate the relevant subpopulation from the parent suspensions. Compared with the method of modulating the thickness of the phospholipid film without centrifugation, nanobubbles fabricated under optimal centrifugation conditions exhibited a uniform bubble size, good stability, and low toxicity. Using in vitro ultrasound imaging, nanobubbles displayed excellent enhancement ability, which was comparable to microbubbles. In an in vivo experiment, the video intensity of nanobubbles in tumors was stronger than that of microbubbles at different times (5 min, 163.5 ± 8.3 a.u. vs. 143.2 ± 7.5 a.u., P < 0.01; 15 min, 125.4 ± 5.2 a.u. vs. 97.3 ± 4.6 a.u., P < 0.01). Fluorescence imaging obtained by confocal laser scanning microscopy demonstrated that obviously more nanobubbles passed through the vessel wall into the extravascular and intercellular space of tumors, compared with microbubbles. In conclusion, this optimized preparation method will strongly promote the application of nanobubbles in imaging and therapy.

Ultrasound with Microbubble Contrast Agent and Urokinase for Thrombosis

This study was aimed at assessing the effects of urokinase (UK) in combination with ultrasound and microbubbles in in vitro and in vivo thrombolytic therapy for the treatment of deep vein thrombosis (DVT). Thrombi with formation times of 1, 3, 7, 14 and 21 d were used for thrombolysis. Forty-five adult mongrel dogs were used to evaluate thrombosis in vivo. Both in vitro and in vivo analyses revealed that UK + microbubbles had the best effect among the combinations. Thrombolysis <7 d was more effective at a thrombolysis rate of about 50%, but the thrombolytic effect of thrombi >7 d was poor at thrombolysis rates <30%. Ultrasound + UK significantly increased the thrombolysis rate of thrombi <7 d. These results suggest that the combination of ultrasound with microbubble contrast agents and UK may have a synergistic effect on thrombolysis.

Recent strategies on targeted delivery of thrombolytics

Thrombus formed in blood vessel is a progressive process, which would lead to life-threatening thrombotic diseases such as ischemic stroke. Unlike other diseases, the recognition of thrombus is usually in the late stage where blood vessels are largely blocked. So acute thrombotic diseases have a narrow therapeutic window, and remain leading causes of morbidity and mortality, whereas current thrombolysis therapy has limited therapeutic effects and bleeding complications. Thrombolytic agents in unwanted sites would cause hemorrhage due to the activation of plasminogen. Moreover, untargeted thrombolysis therapy require large amounts of thrombolytic agents, which in return would enhance hemorrhage risk. To improve the efficiency while minimizing the adverse effects of traditional thrombolysis therapy, novel drug delivery systems have been investigated. Various targeting strategies including ultrasound and magnetic field directed targeting, and specific binding, have been designed to deliver thrombolytic drugs to the thrombotic sites. These strategies demonstrate promising results in reducing bleeding risk as well as allowing less dosage of thrombolytic drugs with lowered clot lysis time. In this review, we discuss recent progress on targeted delivery of thrombolytics, and summarize treatment advantages and shortcomings, potentially helping to further promote the development of targeted thrombolysis.

[Efficacy of combined ultrasound and microbubble treatment for thrombolysis for rescuing ischemic tissues in rats at different time after thrombosis]

OBJECTIVE

To explore the relationship between the time after thrombosis and the efficacy of combined ultrasound and microbubble treatment for rescuing the ischemic tissues.

METHODS

Rat models of thrombosis in the right common iliac artery were established and received combined ultrasound and microbubble treatment at 3, 6 and 12 h after thrombosis. The recanalization rate of the right common iliac artery was assessed using both 2-dimensional and Doppler ultrasound. The plateau acoustic intensity (AI) was quantified for estimating the skeletal microvascular blood volume, and skeletal muscle injury markers including myoglobin (Mb) and creatinine kinase (CK) were measured using ELISA. Postmortem TUNEL staining was used to detect the apoptotic rate of skeletal muscle cells in the hind limb of the rats.

RESULTS

Compared with those in 3 h group, the recanalization rate and AI were significantly lower, and the levels of Mb and CK and the apoptotic rate of the skeletal muscle cells were significantly higher in both 6 h group and 12 h group (P < 0.05). Compared with those in 6 h group, the rats receiving treatment at 12 h after thrombosis showed significantly lowered AI and increased Mb, CK and apoptotic rate of the skeletal muscle cells (P < 0.05).

CONCLUSIONS

The efficacy of combined ultrasound and microbubble treatment for rescuing ischemic tissues tends to be attenuated as the time after thrombosis prolongs in rats.

In vivo evaluation of urokinase-loaded hollow nanogels for sonothrombolysis on suture embolization-induced acute ischemic stroke rat model

The urokinase-type plasminogen activator (uPA) loaded hollow nanogels (nUK) were synthesized by a one-step reaction of glycol chitosan and aldehyde capped poly (ethylene oxide). The resultant formulation is sensitive to diagnostic ultrasound (US) of 2 MHz. Herein, we evaluated the in vivo sonothrombolysis performance of the nUK on acute ischemic stroke rat model which was established by suture embolization of middle cerebral artery (MCA). Via intravenous (i.v.) administration, the experimental data prove a controlled release of the therapeutic protein around the clots under ultrasound stimulation, leading to enhanced thrombolysis efficiency of the nUK, evidenced from smaller infarct volume and better clinical scores when compared to the i.v. dose of free uPA no matter with or without US intervention. Meanwhile, the preservation ability of the nanogels not only prolonged the circulation duration of the protein, but also resulted in the better blood-brain barrier protection of the nUK formulation, showing no increased risk on the hemorrhagic transformation than the controls. This work suggests that the nUK is a safe sonothrombolytic formulation for the treatment of acute ischemic stroke.

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Ultrasonic responsive urokinase (uPA)-loaded hollow nanogels (nUK) were synthesized for stroke treatment.

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Acute ischemic stroke rat model was established by suture embolization of middle cerebral artery.

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The nUK enhanced the sonothrombolytic efficacy and led to better BBB protection compared to the free uPA.