Deep Penetration of Targeted Nanobubbles Enhanced Cavitation Effect on Thrombolytic Capacity

Cutting-edge advances in nano/biomedicine: A review on transforming thrombolytic therapy

Thrombotic blockages within blood vessels give rise to critical cardiovascular disorders, including ischemic stroke, venous thromboembolism, and myocardial infarction. The current approach to the therapy of thrombolysis involves administering Plasminogen Activators (PA), but it is hindered by fast drug elimination, narrow treatment window, and the potential for bleeding complications. Leveraging nanomedicine to encapsulate and deliver PA offers a solution by improving the efficacy of therapy, safeguarding the medicine from proteinase biodegradation, and reducing unwanted effects in in vivo trials. In this review, we delve into the underlying venous as well as arterial thrombus pathophysiology and provide an overview of clinically approved PA used to address acute thrombotic conditions. We explore the existing challenges and potential directions within recent pivotal research on a variety of targeted nanocarriers, such as lipid, polymeric, inorganic, and biological carriers, designed for precise delivery of PA to specific sites. We also discuss the promising role of microbubbles and ultrasound-assisted Sono thrombolysis, which have exhibited enhanced thrombolysis in clinical studies. Furthermore, our review delves into approaches for the strategic development of nano-based carriers tailored for targeting thrombolytic action and efficient encapsulation of PA, considering the intricate interaction in biology systems as well as nanomaterials. In conclusion, the field of nanomedicine offers a valuable method for the exact and effective therapy of severe thrombus conditions, presenting a pathway toward improved patient outcomes and reduced complications.

Histotripsy and Catheter-Directed Lytic: Efficacy in Highly Retracted Porcine Clots In Vitro

OBJECTIVE

Standard treatment for deep vein thrombosis (DVT) involves catheter-directed anticoagulants or thrombolytics, but the chronic thrombi present in many DVT cases are often resistant to this therapy. Histotripsy has been found to be a promising adjuvant treatment, using the mechanical action of cavitating bubble clouds to enhance thrombolytic activity. The objective of this study was to determine if histotripsy enhanced recombinant tissue plasminogen activator (rt-PA) thrombolysis in highly retracted porcine clots in vitro in a flow model of occlusive DVT.

METHODS

Highly retracted porcine whole blood clots were treated for 1 h with either catheter-directed saline (negative control), rt-PA (lytic control), histotripsy, DEFINITY and histotripsy or the combination of rt-PA and histotripsy with or without DEFINITY. Five-cycle, 1.5 MHz histotripsy pulses with a peak negative pressure of 33.2 MPa and pulse repetition frequency of 40 Hz were applied along the clot. B-Mode and passive cavitation images were acquired during histotripsy insonation to monitor bubble activity.

RESULTS

Clots subjected to histotripsy with and without rt-PA exhibited greater thrombolytic efficacy than controls (7.0% flow recovery or lower), and histotripsy with rt-PA was more efficacious than histotripsy with saline (86.1 ± 10.2% compared with 61.7 ± 19.8% flow recovery). The addition of DEFINITY to histotripsy with or without rt-PA did not enhance either thrombolytic efficacy or cavitation dose. Cavitation dose generally did not correlate with thrombolytic efficacy.

CONCLUSION

Enhancement of thrombolytic efficacy was achieved using histotripsy, with and without catheter-directed rt-PA, in the presence of physiologic flow. This suggests these treatments may be effective as therapy for DVT.

Beyond silence: evolving ultrasound strategies in the battle against cardiovascular thrombotic challenges

Cardiovascular thrombotic events have long been a perplexing factor in clinical settings, influencing patient prognoses significantly. Ultrasound-mediated acoustic therapy, an innovative thrombolytic treatment method known for its high efficiency, non-invasiveness, safety, and convenience, has demonstrated promising potential for clinical applications and has gradually become a focal point in cardiovascular thrombotic disease research. The current challenge lies in the technical complexities of preparing ultrasound-responsive carriers with thrombus-targeting capabilities and high thrombolytic efficiency. Additionally, optimizing the corresponding acoustic treatment mode is crucial to markedly enhance the thrombolytic effectiveness of ultrasound-mediated acoustic therapy. In light of the current status, this article provides a comprehensive review of the research progress in innovative ultrasound-mediated acoustic therapy for cardiovascular thrombotic diseases. It explores the impact of technical methods, therapeutic mechanisms, and influencing factors on the thrombolytic efficiency and clinical potential of ultrasound-mediated acoustic therapy. The review places particular emphasis on identifying solutions and key considerations in addressing the challenges associated with this cutting-edge therapeutic approach.

Dual-mode nanoprobe strategy integrating ultrasound and near-infrared light for targeted and synergistic arterial thrombolysis

Efficient thrombolysis in time is crucial for prognostic improvement of patients with acute arterial thromboembolic disease, while limitations and complications still exist in conventional thrombolytic treatment methods. Herein, our study sought to investigate a novel dual-mode strategy that integrated ultrasound (US) and near-infrared light (NIR) with establishment of hollow mesoporous silica nanoprobe (HMSN) which contains Arginine-glycine-aspartate (RGD) peptide (thrombus targeting), perfluoropentane (PFP) (thrombolysis with phase-change and stable cavitation) and indocyanine green (ICG) (thrombolysis with photothermal conversion). HMSN is used as the carrier, the surface is coupled with targeted RGD to achieve high targeting and permeability of thrombus, PFP and ICG are loaded to achieve the collaborative diagnosis and treatment of thrombus by US and NIR, so as to provide a new strategy for the integration of diagnosis and treatment of arterial thrombus. From the in vitro and in vivo evaluation, RGD/ICG/PFP@HMSN can aggregate and penetrate at the site of thrombus, and finally establish the dual-mode directional development and thrombolytic treatment under the synergistic effect of US and NIR, providing strong technical support for the accurate diagnosis and treatment of arterial thrombosis.

Current Status of Sub-micron Cavitation-Enhancing Agents for Sonothrombolysis

Thrombosis in cardiovascular disease is an urgent global issue, but treatment progress is limited by the risks of current antithrombotic approaches. The cavitation effect in ultrasound-mediated thrombolysis offers a promising mechanical alternative for clot lysis. Further addition of microbubble contrast agents introduces artificial cavitation nuclei that can enhance the mechanical disruption induced by ultrasound. Recent studies have proposed sub-micron particles as novel sonothrombolysis agents with increased spatial specificity, safety and stability for thrombus disruption. In this article, the applications of different sub-micron particles for sonothrombolysis are discussed. Also reviewed are in vitro and in vivo studies that apply these particles as cavitation agents and as adjuvants to thrombolytic drugs. Finally, perspectives on future developments in sub-micron agents for cavitation-enhanced sonothrombolysis are shared.

Targeted microbubbles combined with low-power focused ultrasound promote the thrombolysis of acute deep vein thrombosis

Introduction: The side effects of conventional therapy for acute deep vein thrombosis (DVT) are severe, with inflammatory reactions playing a pivotal role. It is particularly important to explore new ways of treatment thrombosis by targeting inflammatory factors.

Methods: A targeted microbubble contrast agent was prepared using the biotin-avidin method. The 40 DVT model rabbits were established and divided into four groups according to different treatment regimens. The four coagulation indexes, TNF-α, and D-dimer content of experimental animals were measured before modeling and before and after treatment, and the thrombolysis was assessed by ultrasound imaging. Finally, the results were verified by pathology.

Results and Discussion: Fluorescence microscopy verified the successful preparation of targeted microbubbles. Among the groups, PT, APTT, and TT in Group II-IV were longer than those in Group I (all p < 0.05). FIB and D-dimer content were lower than those in Group I (all p < 0.05), and TNF-α content in Group IV was lower than that in Group I-III (all p < 0.05). Pairwise comparison before modeling and before treatment and after treatment showed that, after treatment, the PT, APTT, and TT in Group II-IV were longer than those before modeling (all p < 0.05). The contents of FIB and D-dimer were lower than those before modeling and before treatment (all p < 0.05). The content of TNF-α decreased significantly only in Group IV, but increased in the other three groups. Targeted microbubbles combined with Low-power focused ultrasound can reduce inflammation, significantly promote thrombolysis, and provide new ideas and methods for the diagnosis and treatment of acute DVT.

Poly-α, β-d, l-Aspartyl-Arg-Gly-Asp-Ser-Based Urokinase Nanoparticles for Thrombolysis Therapy

The most concerning adverse effects of thrombolytic agents are major bleeding and intracranial hemorrhage due to their short half-life, low fibrin specificity, and high dosage. To alleviate bleeding side effects during thrombolytic therapy which would bring about the risk of aggravation, we try to find a novel biodegradable delivery nanosystem to carry drugs to target the thrombus, reduce the dosage of the drug, and system side effects. A novel urokinase/poly-α, β-d, l-aspartyl-Arg-Gly-Asp-Ser complex (UK/PD-RGDS) was synthesized and simply prepared. Its thrombolytic potency was assayed by the bubble-rising method and in vitro thrombolytic activity by the thrombus clot lysis assay separately. The in vivo thrombolytic activity and bleeding complication were evaluated by a rat model of carotid arteriovenous bypass thrombolysis. The thrombolytic potency (1288.19 ± 155.20 U/mg) of the UK/PD-RGDS complex nano-globule (18-130 nm) was 1.3 times that of commercial UK (966.77 ± 148.08 U/mg). In vivo, the UK/PD-RGDS complex (2000 IU/kg) could reduce the dose of UK by 90% while achieving the equivalent thrombolysis effect as the free UK (20,000 IU/kg). Additionally, the UK/PD-RGDS complex decreased the tail bleeding time compared with UK. The organ distribution of the FITC-UK/PD-RGDS complex was explored in the rat model. The UK/PD-RGDS complex could provide a promising platform to enhance thrombolytic efficacy significantly and reduce the major bleeding degree.

Advances in nanomaterial-based targeted drug delivery systems

Nanomaterial-based drug delivery systems (NBDDS) are widely used to improve the safety and therapeutic efficacy of encapsulated drugs due to their unique physicochemical and biological properties. By combining therapeutic drugs with nanoparticles using rational targeting pathways, nano-targeted delivery systems were created to overcome the main drawbacks of conventional drug treatment, including insufficient stability and solubility, lack of transmembrane transport, short circulation time, and undesirable toxic effects. Herein, we reviewed the recent developments in different targeting design strategies and therapeutic approaches employing various nanomaterial-based systems. We also discussed the challenges and perspectives of smart systems in precisely targeting different intravascular and extravascular diseases.

Nanodroplet-Coated Microbubbles Used in Sonothrombolysis with Two-Step Cavitation Strategy

Thrombosis is a major cause of morbidity and mortality and sonothrombolysis is a promising method for its treatment. However, the slow diffusion of the thrombolytic agents into the thrombus results in slow recanalization. Here, nanodroplet-coated microbubbles (NCMBs) are designed and fabricated and a two-step cavitation strategy is used to accelerate the thrombolysis. The first cavitation of the NCMBs, cavitation and collapse of the microbubbles induced by low frequency ultrasound, drives the nanodroplets on the shell into the thrombus, while the second cavitation, the phase-change and volume expansion of drug-loaded nanodroplets triggered by high frequency ultrasound, loosens the thrombus by the sono-porosity effect. This two-step cavitation of the NCMBs is verified using a fibrin agarose model, where a rapid diffusion of the thrombolytic agents is observed. Furthermore, the NCMBs reach much higher thrombolysis efficiency in both in vitro and proof-of-concept experiments performed with living mice. The nanodroplet-coated microbubbles are a promising diffusion medicines carrier for efficient drug delivery.

Binding properties of flowing fibrin-targeted microbubbles evaluated with a thrombus-embedded microchannel

Fibrin is found in both arterial and venous thrombi, which provides an important target for thrombus-targeted microbubbles (MBs) used in MB-enhanced ultrasound imaging and sonothrombolysis. A fibrin-targeted peptide, Cys-Arg-Glu-Lys-Ala (CREKA), is used to modify the commercially available SonoVue ultrasound contrast agent using a conjugation method, and the binding capacity and binding strength of the fibrin-targeted CREKA-modified SonoVue MBs are evaluated with a thrombus-embedded microchannel at a typical shear rate range of venous and arterial blood flow. The experimental results indicate that the targeted MBs bind firmly to the thrombus surface when they flow along the microchannel at a wall shear rate of up to 1000 s^-1. This work not only provides an effective method for the fabrication of fibrin-targeted MBs based on commercially available SonoVue MBs but also demonstrates an approach for evaluation of the binding properties of flowing targeted MBs under well-controlled flow conditions.

The Updated Role of Transcranial Ultrasound Neuromodulation in Ischemic Stroke: From Clinical and Basic Research

Ischemic stroke is a common cause of death and disability worldwide, which leads to serious neurological and physical dysfunction and results in heavy economic and social burdens. For now, timely and effective dissolution of thrombus, and ultimately improvement in the recovery of neurological functions, is the treatment strategy focus. Recently, many studies have reported that transcranial ultrasound stimulation (TUS), as a non-invasive method, can dissolve thrombus, improve cerebral blood circulation, and exert a neuroprotective effect post-stroke. TUS can promote functional recovery and improve rehabilitation efficacy among patients with ischemic stroke. This mini-review summarizes the potential mechanism and limitation of TUS in stroke aims to provide a new strategy for the future treatment of patients with ischemic stroke.

Enhancing Cancer Immunotherapeutic Efficacy with Sonotheranostic Strategies

Immunotherapy has revolutionized the modality for establishing a firm immune response and immunological memory. However, intrinsic limitations of conventional low responsive poor T cell infiltration and immune related adverse effects urge the coupling of cancer nanomedicines with immunotherapy for boosting antitumor response under ultrasound (US) sensitization to mimic dose-limiting toxicities for safe and effective therapy against advanced cancer. US is composed of high-frequency sound waves that mediate targeted spatiotemporal control over release and internalization of the drug. The unconventional US triggered immunogenic nanoengineered arena assists the limited immunogenic dose, limiting toxicities and efficacies. In this Review, we discuss current prospects of enhanced immunotherapy using nanomedicine under US. We highlight how nanotechnology designs and incorporates nanomedicines for the reprogramming of systematic immunity in the tumor microenvironment. We also emphasize the mechanical and biological potential of US, encompassing sonosensitizer activation for enhanced immunotherapeutic efficacies. Finally, the smartly converging combinational platform of US stimulated cancer nanomedicines for amending immunotherapy is summarized. This Review will widen scientists' ability to explore and understand the limiting factors for combating cancer in a precisely customized way.

Magneto-sonothrombolysis with combination of magnetic microbubbles and nanodroplets

This paper reports a novel technique using the rotational magnetic field oscillation and low-intensity sub-megahertz ultrasound stimulation of magnetic microbubbles (MMBs) to promote the nanodroplets (NDs) phase transition and improve the permeation of NDs into the blood clot fibrin network to enhance the sonothrombolysis efficiency. In this study, the influence of different treatment methods with a combination of MMBs and NDs on the thrombolysis rate of both unretracted and retracted clots were investigated, including the stable and inertial cavitation, tPA effects, MMBs/NDs concentration ratio, sonication factors (input voltage, duty cycle) and rotational magnetic field factors (flux density, frequency). We demonstrated that tPA-mediated magneto-sonothrombolysis in combining NDs with MMBs could significantly enhance in vitro lysis of both unretracted clots (85 ± 8.3%) and retracted clots (57 ± 6.5%) in a flow model with 30 min treatment. The results showed that the combination of MMBs and NDs substantially improves in vitro lysis of blood clots with an unprecedented lysis rate.

Liposomes-based nanoplatform enlarges ultrasound-related diagnostic and therapeutic precision

Ultrasound (US) is notable in the medical field as a safe and effective imaging modality due to its lack of ionizing radiation, non-invasive approach, and real-time monitoring capability. Accompanying recent progress in nanomedicine, US has been providing hope of theranostic capability not only for imaging-based diagnosis but also for US-based therapy by taking advantage of the bioeffects induced by US. Cavitation, sonoporation, thermal effects, and other cascade effects stimulated by acoustic energy conversion have contributed to medical problem-solving in the past decades although to varying degrees of efficacy in comparisons to other methods. Recently, the usage of liposomes-based nanoplatform fuels the development of nanomedicine and provides novel clinical strategies for antitumor, thrombolysis, and controlled drug release. Merging of novel liposome-based nanoplatforms and US-induced reactions has promise for a new blueprint for future medicine. In the present review article, the value of liposome-based nanoplatforms in US-related diagnosis and therapy will be discussed and summarized along with potential future directions for further investigations.

Ultrasound-Responsive Nanopeptisomes Enable Synchronous Spatial Imaging and Inhibition of Clot Growth in Deep Vein Thrombosis

Deep vein thrombosis (DVT) is a life-threatening blood clotting condition that, if undetected, can cause deadly pulmonary embolisms. Critical to its clinical management is the ability to rapidly detect, monitor, and treat thrombosis. However, current diagnostic imaging modalities lack the resolution required to precisely localize vessel occlusions and enable clot monitoring in real time. Here, we rationally design fibrinogen-mimicking fluoropeptide nanoemulsions, or nanopeptisomes (NPeps), that allow contrast-enhanced ultrasound imaging of thrombi and synchronous inhibition of clot growth. The theranostic duality of NPeps is imparted via their intrinsic binding to integrins overexpressed on platelets activated during coagulation. The platelet-bound nanoemulsions can be vaporized and oscillate in an applied acoustic field to enable contrast-enhanced Doppler ultrasound detection of thrombi. Concurrently, nanoemulsions bound to platelets competitively inhibit secondary platelet-fibrinogen binding to disrupt further clot growth. Continued development of this synchronous theranostic platform may open new opportunities for image-guided, non-invasive, interventions for DVT and other vascular diseases.

Nanodroplet-mediated catheter-directed sonothrombolysis of retracted blood clots

One major challenge in current microbubble (MB) and tissue plasminogen activator (tPA)-mediated sonothrombolysis techniques is effectively treating retracted blood clots, owing to the high density and low porosity of retracted clots. Nanodroplets (NDs) have the potential to enhance retracted clot lysis owing to their small size and ability to penetrate into retracted clots to enhance drug delivery. For the first time, we demonstrate that a sub-megahertz, forward-viewing intravascular (FVI) transducer can be used for ND-mediated sonothrombolysis, in vitro. In this study, we determined the minimum peak negative pressure to induce cavitation with low-boiling point phase change nanodroplets and clot lysis. We then compared nanodroplet mediated sonothrombolysis to MB and tPA mediate techniques. The clot lysis as a percent mass decrease in retracted clots was 9 ± 8%, 9 ± 5%, 16 ± 5%, 14 ± 9%, 17 ± 9%, 30 ± 8%, and 40 ± 9% for the control group, tPA alone, tPA + US, MB + US, MB + tPA + US, ND + US, and ND + tPA + US groups, respectively. In retracted blood clots, combined ND- and tPA-mediated sonothrombolysis was able to significantly enhance retracted clot lysis compared with traditional MB and tPA-mediated sonothrombolysis techniques. Combined nanodroplet with tPA-mediated sonothrombolysis may provide a feasible strategy for safely treating retracted clots.

Concurrent visual and acoustic tracking of passive and active delivery of nanobubbles to tumors

Background: There has been growing interest in nanobubbles for their potential to extend bubble-mediated ultrasound approaches beyond that of their larger microbubble counterparts. In particular, the smaller scale of nanobubbles may enable them to access the tumor extravascular compartment for imaging and therapy in closer proximity to cancer cells. Compelling preliminary demonstrations of the imaging and therapeutic abilities of nanobubbles have thus emerged, with emphasis on their ability to extravasate. However, studies to date rely on indirect histologic evidence that cannot confirm whether the structures remain intact beyond the vasculature - leaving their extravascular potential largely untapped.

Methods: Nanobubble acoustic scattering was assessed using a recently reported ultra-stable formulation at low concentration (10⁶ mL^-1) and frequency (1 MHz), over a range of pressures (100-1500 kPa) in a channel phantom. The pressure-dependent response was utilized as a basis for in vivo experiments where ultrasound transmitters and receivers were integrated into a window chamber for simultaneous intravital multiphoton microscopy and acoustic monitoring in tumor-affected microcirculation. Microscopy and acoustic data were utilized to assess passive and active delivery of nanobubbles and determine whether they remained intact beyond the vasculature.

Results: Nanobubbles exhibit pressure-dependent nonlinear acoustic scattering. Nanobubbles are also found to have prolonged acoustic vascular pharmacokinetics, and passively extravasate intact into tumors. Ultrasound stimulation of nanobubbles is shown to actively enhance the delivery of both intact nanobubbles and shell material, increasing their spatial bioavailability deeper into the extravascular space. A range of acute vascular effects were also observed.

Conclusion: This study presents the first direct evidence that nanobubbles passively and actively extravasate intact in tumor tissue, and is the first to directly capture acute vascular events from ultrasound-stimulation of nanobubbles. The insights gained here demonstrate an important step towards unlocking the potential of nanobubbles and extending ultrasound-based applications.

Recent advances in micro- and nano-bubbles for atherosclerosis applications

Micro- and nano-bubbles have been developed as powerful multimodal theranostic agents for atherosclerosis treatment.