Ultrasound contrast agents nucleate inertial cavitation in vitro

Delivery of Cavitation Therapy With a Modified Clinical Scanner: In Vitro Evaluation

In this study, we design and implement pulses [1.67 MHz, 20-1000 cycles, 0.8-2.5 MPa, and 5-100 ms pulse repetition time (PRT)] suitable for microbubble cavitation treatments with a phased array of a clinical ultrasound scanner. A range of acoustic parameters was evaluated in a tissue-mimicking phantom with suspended Sonazoid microbubbles. Hydrophone measurements were used to optimize the transmit beamforming. A passive cavitation detection (PCD) system was designed to measure the microbubble scattered signals over a 1 s exposure. Postprocessing of the scattered signals evaluated frequency content to extract broadband energy and calculate the inertial cavitation dose (ICD). ICD was maximized at 1000 cycles (maximum pulse length), 5 ms (fastest firing rate), and 2.5 MPa peak negative pressure (PNP) (maximum pressure). Inertial cavitation was only sustained for about three pulses (out of hundreds fired) occurring within the first 100 ms of treatment. Temporal analysis of the first 1000-cycle pulse revealed that broadband energy is sustained for the entire pulse. We also demonstrate that while inertial cavitation is possible with clinically available pulse wave Doppler settings, ICD can be significantly increased using the new conditions suggested in this work. We have delivered successful image-guided cavitation treatment after modifying a clinical scanner and monitored the cavitation dose with a PCD system on a gel phantom with suspended microbubbles. We plan to apply this technique in vivo in animal tumor models next. This work demonstrates the first implementation of long, high-pressure pulses on a clinical scanner that users can optimize for cavitation treatments.

Ultrasound stimulated perfluorobutane microbubbles cavitation enhanced the therapeutic effect of colchicine in rats with acute gouty arthritis

Objective

This study aimed to explore whether cavitation generated by ultrasound-stimulated microbubbles (USMB) can enhance the therapeutic efficacy of colchicine and diminish its gastrointestinal side effects in rats with acute gouty arthritis (AGA).

Materials and methods

The rat AGA model was established by injection of Monosodium urate (MSU) crystals. The rats were randomly divided into 6 groups (A: control group, B: model control group, C: cavitation group, D: high dose colchicine group, E: cavitation + low dose colchicine group, F: cavitation + high dose colchicine group) according to whether they were given cavitation and different doses of colchicine. The effect of cavitation on blood perfusion was analyzed by comparing contrast-enhanced ultrasound (CEUS) and the area under the curve (AUC) of CEUS with the ankle joint of right hind limb. The AGA symptoms were assessed by referring to the degree of ankle joint swelling within 24 h and the gait score. The infiltration of neutrophils was determined using the hematoxylin-eosin (HE) staining method. For the evaluation of vascular inflammation and dilation, plasma interleukin-1β (IL-1β) and endothelial nitric oxide synthase (eNOS) served as the key indicators. Besides, the severity of gastrointestinal adverse reactions is determined by analyzing the gastrointestinal reaction scores.

Results

When compared with groups A, B, and D, the AUC was markedly higher in groups C, E, and F (all P < 0.05). In groups E and F, the degree of ankle swelling, gait scores, and the level of plasma IL-1β in AGA rats were lower, while the concentration of plasma eNOS was higher compared to the group D (all P < 0.05). HE staining findings demonstrated that the integration of cavitation and colchicine played a positive role in reducing neutrophil infiltration in the ankle joint synovium and mitigating the gastrointestinal reaction score in AGA rats. In contrast to groups D, E, and F that were given colchicine, group E had a substantially lower gastrointestinal reaction score, with statistically significant differences observed in pairwise comparisons (all P < 0.05).

Conclusion

In rats with AGA, cavitation generated by USMB exerted a remarkable effect on augmenting the blood perfusion of the ankle joint. This, in turn, not only amplified the anti-gout efficacy of colchicine but also reduced the dosage of colchicine. Concurrently, it effectively mitigated the associated gastrointestinal side effects.

From concept to early clinical trials: 30 years of microbubble-based ultrasound-mediated drug delivery research

Ultrasound mediated drug delivery, a promising therapeutic modality, has evolved remarkably over the past three decades. Initially designed to enhance contrast in ultrasound imaging, microbubbles have emerged as a main vector for drug delivery, offering targeted therapy with minimized side effects. This review addresses the historical progression of this technology, emphasizing the pivotal role microbubbles play in augmenting drug extravasation and targeted delivery. We explore the complex mechanisms behind this technology, from stable and inertial cavitation to diverse acoustic phenomena, and their applications in medical fields. While the potential of ultrasound mediated drug delivery is undeniable, there are still challenges to overcome. Balancing therapeutic efficacy and safety and establishing standardized procedures are essential areas requiring attention. A multidisciplinary approach, gathering collaborations between researchers, engineers, and clinicians, is important for exploiting the full potential of this technology. In summary, this review highlights the potential of using ultrasound mediated drug delivery in improving patient care across various medical conditions.

State of the art on microbubble cavitation monitoring and feedback control for blood-brain-barrier opening using focused ultrasound

Focused ultrasound (FUS) is a non-invasive and highly promising method for targeted and reversible blood-brain barrier permeabilization. Numerous preclinical studies aim to optimize the localized delivery of drugs using this method in rodents and non-human primates. Several clinical trials have been initiated to treat various brain diseases in humans using simultaneous BBB permeabilization and drug injection. This review presents the state of the art ofin vitroandin vivocavitation control algorithms for BBB permeabilization using microbubbles (MB) and FUS. Firstly, we describe the different cavitation states, their physical significance in terms of MB behavior and their translation into the spectral composition of the backscattered signal. Next, we report the different indexes calculated and used during the ultrasonic monitoring of cavitation. Finally, the differentin vitroandin vivocavitation control strategies described in the literature are presented and compared.

Enhancing cavitation dynamics and its mechanical effects with dual-frequency ultrasound

Objective. Acoustic cavitation and its mechanical effects (e.g. stress and strain) play a primary role in ultrasound applications. Introducing encapsulated microbubbles as cavitation nuclei and utilizing dual-frequency ultrasound excitation are highly effective approaches to reduce cavitation thresholds and enhance cavitation effects. However, the cavitation dynamics of encapsulated microbubbles and the resultant stress/strain in viscoelastic tissues under dual-frequency excitation are poorly understood, especially for the enhancement effects caused by a dual-frequency approach. The goal of this study was to numerically investigate the dynamics of a lipid-coated microbubble and the spatiotemporal distributions of the stress and strain under dual-frequency excitation. Approach. The Gilmore–Zener bubble model was coupled with a shell model for the nonlinear changes of both shell elasticity and viscosity to accurately simulate the cavitation dynamics of lipid-coated microbubbles in viscoelastic tissues. Then, the spatiotemporal evolutions of the cavitation-induced stress and strain in the surrounding tissues were characterized quantitatively. Finally, the influences of some paramount parameters were examined to optimize the outcomes. Main results. We demonstrated that the cavitation dynamics and associated stress/strain were prominently enhanced by a dual-frequency excitation, highlighting positive correlations between the maximum bubble expansion and the maximum stress/strain. Moreover, the results showed that the dual-frequency ultrasound with smaller differences in its frequencies and pressure amplitudes could enhance the bubble oscillations and stress/strain more efficiently, whereas the phase difference manifested small influences under these conditions. Additionally, the dual-frequency approach seemed to show a stronger enhancement effect with the shell/tissue viscoelasticity increasing to a certain extent. Significance. This study might contribute to optimizing the dual-frequency operation in terms of cavitation dynamics and its mechanical effects for high-efficient ultrasound applications.

Ultrasound-Induced DNA Damage and Cellular Response: Historical Review, Mechanisms Analysis, and Therapeutic Implications

The biological effects of ultrasound may be classified into thermal and nonthermal mechanisms. The nonthermal effects may be further classified into cavitational and noncavitational mechanisms. DNA damage induced by ultrasound is considered to be related to nonthermal cavitations. For this aspect, many in vitro studies on DNA have been conducted for evaluating the safety of diagnostic ultrasound, particularly in fetal imaging. Technological advancement in detecting DNA damage both in vitro and in vivo have elucidated the mechanism of DNA damage formation and their cellular response. Damage to DNA, and the residual damages after DNA repair are implicated in the biological effects. Here, we discuss the historical evidence of ultrasound on DNA damage and the mechanism of DNA damage formation both in vitro and in vivo, compared with those induced by ionizing radiation. We also offer a commentary on the safety of ultrasound over X-ray-based imaging. Also, understanding the various mechanisms involved in the bioeffects of ultrasound will lead us to alternative strategies for use of ultrasound for therapy.

Ultrasound-Mediated Drug Delivery: Sonoporation Mechanisms, Biophysics, and Critical Factors

Sonoporation, or the use of ultrasound in the presence of cavitation nuclei to induce plasma membrane perforation, is well considered as an emerging physical approach to facilitate the delivery of drugs and genes to living cells. Nevertheless, this emerging drug delivery paradigm has not yet reached widespread clinical use, because the efficiency of sonoporation is often deemed to be mediocre due to the lack of detailed understanding of the pertinent scientific mechanisms. Here, we summarize the current observational evidence available on the notion of sonoporation, and we discuss the prevailing understanding of the physical and biological processes related to sonoporation. To facilitate systematic understanding, we also present how the extent of sonoporation is dependent on a multitude of factors related to acoustic excitation parameters (ultrasound frequency, pressure, cavitation dose, exposure time), microbubble parameters (size, concentration, bubble-to-cell distance, shell composition), and cellular properties (cell type, cell cycle, biochemical contents). By adopting a science-backed approach to the realization of sonoporation, ultrasound-mediated drug delivery can be more controllably achieved to viably enhance drug uptake into living cells with high sonoporation efficiency. This drug delivery approach, when coupled with concurrent advances in ultrasound imaging, has potential to become an effective therapeutic paradigm.

Collapse pressure measurement of single hollow glass microsphere using single-beam acoustic tweezer

Microbubbles are widely used in medical ultrasound imaging and drug delivery. Many studies have attempted to quantify the collapse pressure of microbubbles using methods that vary depending on the type and population of bubbles and the frequency band of the ultrasound. However, accurate measurement of collapse pressure is difficult as a result of non-acoustic pressure factors generated by physical and chemical reactions such as dissolution, cavitation, and interaction between bubbles. In this study, we developed a method for accurately measuring collapse pressure using only ultrasound pulse acoustic pressure. Under the proposed method, the collapse pressure of a single hollow glass microsphere (HGM) is measured using a high-frequency (20-40 MHz) single-beam acoustic tweezer (SBAT), thereby eliminating the influence of additional factors. Based on these measurements, the collapse pressure is derived as a function of the HGM size using the microspheres' true density. We also developed a method for estimating high-frequency acoustic pressure, whose measurement using current hydrophone equipment is complicated by limitations in the size of the active aperture. By recording the transmit voltage at the moment of collapse and referencing it against the corresponding pressure, it is possible to estimate the acoustic pressure at the given transmit condition. These results of this study suggest a method for quantifying high-frequency acoustic pressure, provide a potential reference for the characterization of bubble collapse pressure, and demonstrate the potential use of acoustic tweezers as a tool for measuring the elastic properties of particles/cells.

Nanobiotechnology-enabled energy utilization elevation for augmenting minimally-invasive and noninvasive oncology thermal ablation

Depending on the local or targeted treatment, independence on tumor type and minimally-invasive and noninvasive feature, various thermal ablation technologies have been established, but they still suffer from the intractable paradox between safety and efficacy. It has been extensively accepted that improving energy utilization efficiency is the primary means of decreasing thermal ablation power and shortening ablation time, which is beneficial for concurrently improving both treatment safety and treatment efficiency. Recent efforts have been made to receive a significant advance in various thermal methods including non-invasive high-intensity focused ultrasound, minimally-invasive radiofrequency and microwave, and non-invasive and minimally-invasive photothermal ablation, and so on. Especially, various nanobiotechnologies and design methodologies were employed to elevate the energy utilization efficiency for acquiring unexpected ablation outcomes accompanied with tremendously reduced power and time. More significantly, some combined technologies, for example, chemotherapy, photodynamic therapy (PDT), gaseous therapy, sonodynamic therapy (SDT), immunotherapy, chemodynamic therapy (CDT), or catalytic nanomedicine, were used to assist these ablation means to repress or completely remove tumors. We discussed and summarized the ablation principles and energy transformation pathways of the four ablation means, and reviewed and commented the progress in this field including newly developed technology or new material types with a highlight on nanobiotechnology-inspired design principles, and provided the deep insights into the existing problems and development direction. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Mechanisms underlying sonoporation: Interaction between microbubbles and cells

The past several decades have witnessed great progress in "smart drug delivery", an advance technology that can deliver genes or drugs into specific locations of patients' body with enhanced delivery efficiency. Ultrasound-activated mechanical force induced by the interactions between microbubbles and cells, which can stimulate so-called "sonoporation" process, has been regarded as one of the most promising candidates to realize spatiotemporal-controllable drug delivery to selected regions. Both experimental and numerical studies were performed to get in-depth understanding on how the microbubbles interact with cells during sonoporation processes, under different impact parameters. The current work gives an overview of the general mechanism underlying microbubble-mediated sonoporation, and the possible impact factors (e.g., the properties of cavitation agents and cells, acoustical driving parameters and bubble/cell micro-environment) that could affect sonoporation outcomes. Finally, current progress and considerations of sonoporation in clinical applications are reviewed also.

Low-intensity pulsed ultrasound in combination with SonoVue induces cytotoxicity of human renal glomerular endothelial cells via repression of the ERK1/2 signaling pathway

OBJECTIVES

Low-intensity pulsed ultrasound (LIPUS) and SonoVue have been used widely for diagnosis and therapeutic treatment. The effects of LIPUS and SonoVue on the microvascular system and underlying molecular mechanisms have not been established.

METHODS

Cultured human renal glomerular endothelial cells (HRGECs) were treated with 5-min ultrasonic irradiation, 20% SonoVue or the combination of both treatments. Cell proliferation, viablity, and apoptosis were measured by MTT assay, Trypan blue exclusion assay and flow cytometry, respectively. Activation of extracellular regulated protein kinases (ERK) were examined by Western blot.

RESULTS

We found that LIPUS and SonoVue alone do not induce cytotoxicity of HRGECs; however, the combination of the two treatments reduces cell proliferation and increases cell death. In addition, the combination of LIPUS and SonoVue suppressed the activation of ERK 1/2 in HRGRCs. With pretreatment of the inhibitor of ERK1/2 signaling, PD98059, LIPUS, and SonoVue does not induce additional cell death and inhibition of proliferation.

CONCLUSIONS

LIPUS combined with SonoVue induces cytotoxicity of HRGECs via repression of the ERK1/2 signaling pathway.

Ultrasound Combined with Microbubbles Enhances the Effects of Methylprednisolone in Lipopolysaccharide-Induced Human Mesangial Cells

A novel drug delivery system mediated by ultrasound (US) combined with microbubbles (MBs) (US+MB) could improve local drug concentration to enhance its efficacy. To investigate the influence of US+MB on methylprednisolone (MP), the effect of US+MB combined with MP (US+MB+MP) on lipopolysaccharide (LPS)-induced human mesangial cells (HMCs) and the underlying mechanism were explored in this study. The results revealed that HMCs treated with LPS underwent significant proliferation and exhibited an increase in nuclear transcription factor-κB (NF-κB) and transforming growth factor-β1 (TGF-β1) expression and a decrease in cellular apoptosis. This effect was significantly inhibited by MP (30-100 μg/ml), US combined with MBs (3.22 × 107 and 8.05 × 107 bubbles/ml), and US combined with both MBs (1.29 × 107 bubbles/ml) and MP (12 μg/ml) (US+MB1+MP12). The effect of US+MB1+MP12 was better than the effect of 12 μg/ml of MP alone and was similar to the effect of 100 μg/ml of MP. Additionally, the intracellular free MP content was significantly higher in the US+MB1+MP12 group than in the MP12 group. US combined with MBs not only inhibited LPS-induced HMC proliferation and NF-κB and TGF-β1 expression and increased cellular apoptosis but also synergized with the pharmacologic effect of MP. The mechanism is partially due to the US-assisted MB local drug delivery and the anti-inflammatory effect induced by US combined with MBs.

Combining ultrasound and intratumoral administration of doxorubicin-loaded microspheres to enhance tumor cell killing

Melanoma is an incurable disease for which alternative treatments to chemotherapy alone are sought. Here, using a melanoma model, we investigated the antitumor potential of combining ultrasound (US) with poly(lactic-co-glycolic acid) (PLGA) microspheres loaded with doxorubicin (DOX). The aim was to achieve synergistic tumoricidal activity through direct and indirect US-mediated damage of tumor cells combined with sustained and potentially controllable release (when combined with US) of DOX from microspheres. An in vitro release assay demonstrated an ability of US to affect the release kinetics of DOX from DOX-loaded PLGA microspheres by inducing a 12% increase in the rate of release. In vitro viability assays demonstrated that combining US with DOX-loaded PLGA microspheres resulted in synergistic tumor cell (B16-F10 melanoma cells) killing. Melanoma-bearing mice were treated intratumorally with DOX (8 µg)-loaded microspheres and subjected to US treatment at the tumor site. This treatment could significantly extend survival (mean survival (MS) = 22.1 days) compared to untreated mice (MS = 10.4 days) and most other treatments, such as blank microspheres plus US (MS = 11.5 days) and DOX (8 µg)-loaded microspheres alone (MS = 13 days). The findings that immune checkpoint blockade did not significantly extend survival of mice treated with DOX (8 µg)-loaded microspheres plus US, and that tumor-free ("cured") mice were not protected from subsequent tumor rechallenge suggests minimal involvement of the adaptive immune response in the observed antitumor activity. Nevertheless, the synergistic increase in survival of melanoma-challenged mice treated with the combination of US and DOX-loaded microspheres implicates such a treatment methodology as a promising additional tool for combatting otherwise currently incurable cancers.

The synergistic bactericidal effect of vancomycin on UTMD treated biofilm involves damage to bacterial cells and enhancement of metabolic activities

In this study, the synergistic effect of vancomycin, a cell wall synthesis inhibitor, and ultrasound-targeted microbubble destruction (UTMD), on cell viability of Staphylococcus epidermidis, embedded in biofilm, was investigated. Biofilms are the leading causes of antibiotic-resistant bacterial infections of medical implants and prosthetics worldwide. The antibiotic-resistant nature of biofilm-embedded pathogens poses a critical challenge to the medical community. Previously, studies have demonstrated the efficacy of using ultrasound waves and UTMD in circumventing this problem. However, the mechanism(s) underlying this phenomenon was not clear. Here, the present study showed that both ultrasound and UTMD damaged the cell wall structure of S. epidermidis, and floccules and fragments from damaged cells were observed on transmission electron microscope micrograph. However, the cell membrane integrity was not seriously affected by treatments, and the treatment increased the metabolic activity levels of the dormant biofilm-embedded bacteria, detected by confocal laser scanning microscope and flow cytometry, which could make them susceptible to the effect of the antibiotic. Thus, the biological mechanism underlying the efficacy of the combined treatment involving UTMD and vancomycin in the case of S. epidermidis biofilm was dissected, which may be utilized for further investigations on other biofilm pathogens before clinical use.

Removal of ligand-bound liposomes from cell surfaces by microbubbles exposed to ultrasound

Gas-filled microbubbles attached to cell surfaces can interact with focused ultrasound to create microstreaming of nearby fluid. We directly observed the ultrasound/microbubble interaction and documented that under certain conditions fluorescent particles that were attached to the surface of live cells could be removed. Fluorescently labeled liposomes that were larger than 500 nm in diameter were attached to the surface of endothelial cells using cRGD targeting to αvβ3 integrin. Microbubbles were attached to the surface of the cells through electrostatic interactions. Images taken before and after the ultrasound exposure were compared to document the effects on the liposomes. When exposed to ultrasound with peak negative pressure of 0.8 MPa, single microbubbles and groups of isolated microbubbles were observed to remove targeted liposomes from the cell surface. Liposomes were removed from a region on the cell surface that averaged 33.1 μm in diameter. The maximum distance between a single microbubble and a detached liposome was 34.5 μm. Single microbubbles were shown to be able to remove liposomes from over half the surface of a cell. The distance over which liposomes were removed was significantly dependent on the resting diameter of the microbubble. Clusters of adjoining microbubbles were not seen to remove liposomes. These observations demonstrate that the fluid shear forces generated by the ultrasound/microbubble interaction can remove liposomes from the surfaces of cells over distances that are greater than the diameter of the microbubble.

Mechanical and Biological Effects of Ultrasound: A Review of Present Knowledge

Ultrasound is widely used for medical diagnosis and increasingly for therapeutic purposes. An understanding of the bio-effects of sonography is important for clinicians and scientists working in the field because permanent damage to biological tissues can occur at high levels of exposure. Here the underlying principles of thermal mechanisms and the physical interactions of ultrasound with biological tissues are reviewed. Adverse health effects derived from cellular studies, animal studies and clinical reports are reviewed to provide insight into the in vitro and in vivo bio-effects of ultrasound.

Increasing of Blood-Brain Tumor Barrier Permeability through Transcellular and Paracellular Pathways by Microbubble-Enhanced Diagnostic Ultrasound in a C6 Glioma Model

Most of the anticancer agents cannot be efficiently delivered into the brain tumor because of the existence of blood-brain tumor barrier (BTB). The objective of this study was to explore the effect of microbubble-enhanced diagnostic ultrasound (MEUS) on the BTB permeability and the possible mechanism. Glioma-bearing rats were randomized into three groups as follows: the microbubble-enhanced continued diagnostic ultrasound (MECUS) group; the microbubble-enhanced intermittent diagnostic ultrasound (MEIUS) group and the control group. The gliomas were insonicated through the skull with a diagnostic ultrasound and injected with microbubbles through the tail veins. Evans Blue (EB) and dynamic contrast-enhanced-MRI were used to test changes in the BTB permeability. Confocal laser scanning microscopy was used to observe the deposition of the EB in the tumor tissues. The distribution and expression of junctional adhesion molecule-A (JAM-A) and calcium-activated potassium channels (K_Ca channels) were detected by a Western blot, qRT-PCR, and immunohistochemical staining. In the MEUS groups, the EB extravasation (11.0 ± 2.2 μg/g in MECUS group and 17.9 ± 2.3 μg/g in MEIUS group) exhibited a significant increase compared with the control group (5.3 ± 0.9 μg/g). The MEIUS group had more EB extravasation than the MECUS group. The K_trans value of the dynamic contrast-enhanced-MRI in the MEUS groups was higher than that of the control group and correlated strongly with the EB extravasation in the tumor (R² = 0.97). This showed that the K_trans value might be a non-invasive method to evaluate the BTB permeability in rat glioma after microbubble-enhanced ultrasound treatment.Western blot, qRT-PCR and immunohistochemical staining revealed that MEUS increased the K_Ca channels expression and reduced JAM-A expression in glioma. This change was more obvious in the MEIUS group than in the MECUS group. The results demonstrated that MEUS effectively increased the BTB permeability in glioma. The mechanisms might involve the up-regulation of K_Ca channels expression and affecting the formation of tight junctions in the BTB by a reduction of JAM-A expression. These findings might provide some new guidance for glioma drug therapy.

Induction of Apoptosis in U937 Cells by Using a Combination of Bortezomib and Low-Intensity Ultrasound

Background

We scrutinized the feasibility of apoptosis induction in blood cancer cells by means of low-intensity ultrasound and the proteasome inhibitor bortezomib (Velcade).

Material/Methods

Human leukemic monocyte lymphoma U937 cells were subjected to ultrasound in the presence of bortezomib and the echo contrast agent Sonazoid. Two types of acoustic intensity (0.18 W/cm² and 0.05 W/cm²) were used for the experiments. Treated U937 cells were analyzed for viability and levels of early and late apoptosis. In addition, scanning electron microscopy analysis of treated cells was performed.

Results

The percentage of cells that underwent early apoptosis in the group treated with ultrasound and Sonazoid was 8.0±1.31% (intensity 0.18 W/cm²) and 7.0±1.69% (0.05 W/cm²). However, coupling of bortezomib and Sonazoid resulted in an increase in the percentage of cells in the early apoptosis phase, up to 32.50±3.59% (intensity 0.18 W/cm²) and 33.0±4.90% (0.05 W/cm²). The percentage of U937 cells in the late apoptosis stage was not significantly different from that in the group treated with bortezomib only.

Conclusions

Our findings indicate the feasibility of apoptosis induction in blood cancer cells by using a combination of bortezomib, ultrasound contrast agents, and low-intensity ultrasound.

Enhancement and Passive Acoustic Mapping of Cavitation from Fluorescently Tagged Magnetic Resonance-Visible Magnetic Microbubbles In Vivo

Previous work has indicated the potential of magnetically functionalized microbubbles to localize and enhance cavitation activity under focused ultrasound exposure in vitro. The aim of this study was to investigate magnetic targeting of microbubbles for promotion of cavitation in vivo. Fluorescently labelled magnetic microbubbles were administered intravenously in a murine xenograft model. Cavitation was induced using a 0.5-MHz focused ultrasound transducer at peak negative focal pressures of 1.2-2.0 MPa and monitored in real-time using B-mode imaging and passive acoustic mapping. Magnetic targeting was found to increase the amplitude of the cavitation signal by approximately 50% compared with untargeted bubbles. Post-exposure magnetic resonance imaging indicated deposition of magnetic nanoparticles in tumours. Magnetic targeting was similarly associated with increased fluorescence intensity in the tumours after the experiments. These results suggest that magnetic targeting could potentially be used to improve delivery of cavitation-mediated therapy and that passive acoustic mapping could be used for real-time monitoring of this process.

Disruption of Prostate Microvasculature by Combining Microbubble-Enhanced Ultrasound and Prothrombin

Previous studies have shown a unique method to disrupt tumor vasculature using pulsed, high-pressure amplitude therapeutic ultrasound combined with microbubbles. In this study, we attempted to destroy the prostate vasculature of canine prostates using microbubble-enhanced ultrasound (MEUS) and prothrombin. The prostates of 43 male mongrel canines were surgically exposed. Twenty-two prostates were treated using MEUS (n = 11) or MEUS and prothrombin (PMEUS, n = 11). The other 21 prostates, which were treated using microbubbles (n = 7), ultrasound (n = 7) or prothrombin (n = 7) only, served as the controls. Prothrombin was intravenously infused at 20 IU/kg. MEUS was induced using a therapeutic ultrasound device at a peak negative pressure of 4.47 MPa and a microbubble injection. Contrast-enhanced ultrasound was performed to assess the blood perfusion of the prostates. Then, the prostate tissue was harvested immediately after treatment and at 48 hours later for pathological examination. The contrast-enhanced ultrasound peak value of the prostate decreased significantly from 36.2 ± 5.6 to 27.1 ± 6.3 after treatment in the PMEUS group, but it remained unchanged in the other groups. Histological examination found severe microvascular rupture, hemorrhage and thrombosis in both MEUS- and PMEUS-treated prostates immediately after treatment, while disruption in the PMEUS group was more severe than in the MEUS group. Forty-eight hours after treatment, massive necrosis and infiltration of white blood cells occurred in the PMEUS group. This study demonstrated that PMEUS disrupted the normal microvasculature of canine prostates and induced massive necrosis. PMEUS could potentially become a new noninvasive method used for the treatment of benign prostatic hyperplasia.

Unseeded Inertial Cavitation for Enhancing the Delivery of Chemotherapies: A Safety Study

Acoustic cavitation can improve local drug delivery in tumors. Without injected external nucleation agents, initiating inertial cavitation requires high negative pressures, which can lead to biological damage. In the present study, unseeded inertial cavitation was obtained in vivo using confocal beams, and the effect of these exposure conditions was assessed on drug structure and activity, shallow tissues and growth of breast tumors. No change was observed in the structure and cytotoxicity of doxorubicin. Experiments were conducted on healthy rats, exposing the thigh and abdomen. Histologic analyses at 72 h and 2 weeks post-treatment demonstrated a modest impact on tissues. Syngeneic 4 T1 breast tumors in mice were sonicated. Immunohistochemical analyses showed that ultrasound did not impact vascular density, proliferation and apoptosis of cancer cells. In addition, ultrasound did not negatively modify cancer cell spreading to the lungs and bone marrow. This provides evidence that these particular parameters can be used safely in vivo.

Apoptosis Induced by Microbubble-Assisted Acoustic Cavitation in K562 Cells: The Predominant Role of the Cyclosporin A-Dependent Mitochondrial Permeability Transition Pore

Acoustic cavitation of microbubbles has been described as inducing tumor cell apoptosis that is partly associated with mitochondrial dysfunction; however, the exact mechanisms have not been fully characterized. Here, low-intensity pulsed ultrasound (1 MHz, 0.3-MPa peak negative pressure, 10% duty cycle and 1-kHz pulse repetition frequency) was applied to K562 chronic myelogenous leukemia cells for 1 min with 10% (v/v) SonoVue microbubbles. After ultrasound exposure, the apoptotic index was determined by flow cytometry with annexin V-fluorescein isothiocyanate/propidium iodide. In addition, mitochondrial membrane potential (ΔΨm) was determined with the JC-1 assay. Translocation of apoptosis-associated protein cytochrome c was evaluated by Western blotting. We found that microbubble-assisted acoustic cavitation can increase the cellular apoptotic index, mitochondrial depolarization and cytochrome c release in K562 cells, compared with ultrasound treatment alone. Furthermore, mitochondrial dysfunction and apoptosis were significantly inhibited by cyclosporin A, a classic inhibitor of the mitochondrial permeability transition pore; however, the inhibitor of Bax protein, Bax-inhibiting peptide, could not suppress these effects. Our results suggest that mitochondrial permeability transition pore opening is involved in mitochondrial dysfunction after exposure to microbubble-assisted acoustic cavitation. Moreover, the release of cytochrome c from the mitochondria is dependent on cyclosporin A-sensitive mitochondrial permeability transition pore opening, but not formation of the Bax-voltage dependent anion channel complex or Bax oligomeric pores. These data provide more insight into the mechanisms underlying mitochondrial dysfunction induced by acoustic cavitation and can be used as a basis for therapy.

Sonogenetics is a non-invasive approach to activating neurons in Caenorhabditis elegans

A major challenge in neuroscience is to reliably activate individual neurons, particularly those in deeper brain regions. Current optogenetic approaches require invasive surgical procedures to deliver light of specific wavelengths to target cells to activate or silence them. Here, we demonstrate the use of low-pressure ultrasound as a non-invasive trigger to activate specific ultrasonically sensitized neurons in the nematode, Caenorhabditis elegans. We first show that wild-type animals are insensitive to low-pressure ultrasound and require gas-filled microbubbles to transduce the ultrasound wave. We find that neuron-specific misexpression of TRP-4, the pore-forming subunit of a mechanotransduction channel, sensitizes neurons to ultrasound stimulus, resulting in behavioural outputs. Furthermore, we use this approach to manipulate the function of sensory neurons and interneurons and identify a role for PVD sensory neurons in modifying locomotory behaviours. We suggest that this method can be broadly applied to manipulate cellular functions in vivo.

Common optogenetic approaches require surgical procedures to deliver light of specific wavelengths to the target cells. Here the authors demonstrate the use of low-pressure ultrasound as a non-invasive trigger to activate specific neurons in Caenorhabditis elegans and find that the mechanotransduction channel TRP-4 sensitizes cells to the ultrasound stimulus.

Effects of ultrasound frequency and tissue stiffness on the histotripsy intrinsic threshold for cavitation

Histotripsy is an ultrasound ablation method that depends on the initiation of a cavitation bubble cloud to fractionate soft tissue. Previous work has indicated that a cavitation cloud can be formed by a single pulse with one high-amplitude negative cycle, when the negative pressure amplitude directly exceeds a pressure threshold intrinsic to the medium. We hypothesize that the intrinsic threshold in water-based tissues is determined by the properties of the water inside the tissue, and changes in tissue stiffness or ultrasound frequency will have a minimal impact on the histotripsy intrinsic threshold. To test this hypothesis, the histotripsy intrinsic threshold was investigated both experimentally and theoretically. The probability of cavitation was measured by subjecting tissue phantoms with adjustable mechanical properties and ex vivo tissues to a histotripsy pulse of 1-2 cycles produced by 345-kHz, 500-kHz, 1.5-MHz and 3-MHz histotripsy transducers. Cavitation was detected and characterized by passive cavitation detection and high-speed photography, from which the probability of cavitation was measured versus pressure amplitude. The results revealed that the intrinsic threshold (the negative pressure at which probability = 0.5) is independent of stiffness for Young's moduli (E) <1 MPa, with only a small increase (∼2-3 MPa) in the intrinsic threshold for tendon (E = 380 MPa). Additionally, results for all samples revealed only a small increase of ∼2-3 MPa when the frequency was increased from 345 kHz to 3 MHz. The intrinsic threshold was measured to be between 24.7 and 30.6 MPa for all samples and frequencies tested in this study. Overall, the results of this study indicate that the intrinsic threshold to initiate a histotripsy bubble cloud is not significantly affected by tissue stiffness or ultrasound frequency in the hundreds of kilohertz to megahertz range.

The behavior of lipid debris left on cell surfaces from microbubble based ultrasound molecular imaging

Lipid monolayer coated microbubbles are currently being developed to identify vascular regions that express certain surface proteins as part of the new technique of ultrasound molecular imaging. The microbubbles are functionalized with targeting ligands which bind to the desired cells holding the microbubbles in place as the remaining unbound microbubbles are eliminated from circulation. Subsequent scanning with ultrasound can detect the highly reflectant microbubbles that are left behind. The ultrasound scanning and detection process results in the destruction of the microbubble, creating lipid fragments from the monolayer. Here we demonstrate that microbubbles targeted to 4T1 murine breast cancer cells and human umbilical cord endothelial cells leave behind adhered fragments of the lipid monolayer after exposure to ultrasound with peak negative pressures of 0.18 and 0.8MPa. Most of the observed fragments were large enough to be resistant to receptor mediated endocytosis. The fragments were not observed to incorporate into the lipid membrane of the cell over a period of 96min. They were not observed to break into smaller pieces or significantly change shape but they were observed to undergo translation and rotation across the cell surface as the cells migrated over the substrate. These large fragments will apparently remain on the surface of the targeted cells for significant periods of time and need to be considered for their potential effects on blood flow through the microcapillaries and potential for immune system recognition.

The influence of distance between microbubbles on the fluid flow produced during ultrasound exposure

The collapse dynamics of lipid monolayer-coated microbubbles in the clinically-relevant size range under 6 μm in diameter have not been studied directly due to their small size obscuring the collapse visualization. This study investigates the influence of inter-microbubble distance on the shape of lipid debris clouds created by the collapse of the microbubble destroying the microbubble lipid monolayer. The shape was highly influenced by the fluid motion that occurred as the microbubbles collapsed. It was observed that at inter-microbubble distances smaller than 37 μm the microbubbles began to interact with one another resulting in distorted and ellipsoid-shaped debris clouds. At inter-microbubble distances less than 10 μm, significantly elongated debris clouds were observed that extended out from the original microbubble location in a single direction. These distortions show a significant distance-dependent interaction between microbubbles. It was observed that microbubbles in physical contact with one another behaved in the same manner as separate microbubbles less than 10 μm apart creating significantly elongated debris clouds. It can be hypothesized that small inter-microbubble distances influence the microbubble to collapse asymmetrically resulting in the creation of fluid jets that contribute to the formation of debris fields that are elongated in a single direction.

Ultrasound and microbubble-mediated gene delivery in cancer: progress and perspectives

Ultrasound-mediated gene delivery with microbubbles has emerged as an attractive nonviral vector system for site-specific and noninvasive gene therapy. Ultrasound promotes intracellular uptake of therapeutic agents, particularly in the presence of microbubbles, by increasing vascular and cell membrane permeability. Several preclinical studies have reported successful gene delivery into solid tumors with significant therapeutic effects using this novel approach. This review provides background information on gene therapy and ultrasound bioeffects and discusses the current progress and overall perspectives on the application of ultrasound and microbubble-mediated gene delivery in cancer.

Characterization of the dynamic activities of a population of microbubbles driven by pulsed ultrasound exposure in sonoporation

Ultrasound-driven microbubble activities have been exploited to transiently disrupt the cell membrane (sonoporation) for non-viral intracellular drug delivery and gene transfection both in vivo and in vitro. In this study, we investigated the dynamic behaviors of a population of microbubbles exposed to pulsed ultrasound and their impact on adherent cells in terms of intracellular delivery and cell viability. By systematically analyzing the bubble activities at time scales relevant to pulsed ultrasound exposure, we identified two quantification parameters that categorize the diverse bubble activities subjected to various ultrasound conditions into three characteristic behaviors: stable cavitation/aggregation (type I), growth/coalescence and translation (type II) and localized inertial cavitation/collapse (type III). Correlation of the bubble activities with sonoporation outcome suggested that type III behavior resulted in intracellular delivery, whereas type II behavior caused the death of a large number of cells. These results provide useful insights for rational selection of ultrasound parameters to optimize outcomes of sonoporation and other applications that exploit the use of ultrasound-driven bubble activities.

Enhanced tumor uptake and penetration of virotherapy using polymer stealthing and focused ultrasound

Background

Oncolytic viruses are among the most powerful and selective cancer therapeutics under development and are showing robust activity in clinical trials, particularly when administered directly into tumor nodules. However, their intravenous administration to treat metastatic disease has been stymied by unfavorable pharmacokinetics and inefficient accumulation in and penetration through tumors.

Methods

Adenovirus (Ad) was “stealthed” with a new N-(2-hydroxypropyl)methacrylamide polymer, and circulation kinetics were characterized in Balb/C SCID mice (n = 8 per group) bearing human ZR-75-1 xenograft tumors. Then, to noninvasively increase extravasation of the circulating polymer-coated Ad into the tumor, it was coinjected with gas microbubbles and the tumor was exposed to 0.5 MHz focused ultrasound at peak rarefactional pressure of 1.2MPa. These ultrasound exposure conditions were designed to trigger inertial cavitation, an acoustic phenomenon that produces shock waves and can be remotely monitored in real-time. Groups were compared with Student t test or one-way analysis of variance with Tukey correction where groups were greater than two. All statistical tests were two-sided.

Results

Polymer-coating of Ad reduced hepatic sequestration, infection (>8000-fold; P < .001), and toxicity and improved circulation half-life (>50-fold; P = .001). Combination of polymer-coated Ad, gas bubbles, and focused ultrasound enhanced tumor infection >30-fold; (4×10⁶ photons/sec/cm²; standard deviation = 3×10⁶ with ultrasound vs 1.3×10⁵; standard deviation = 1×10⁵ without ultrasound; P = .03) and penetration, enabling kill of cells more than 100 microns from the nearest blood vessel. This led to substantial and statistically significant retardation of tumor growth and increased survival.

Conclusions

Combining drug stealthing and ultrasound-induced cavitation may ultimately enhance the efficacy of a range of powerful therapeutics, thereby improving the treatment of metastatic cancer.

Investigation on the inertial cavitation threshold and shell properties of commercialized ultrasound contrast agent microbubbles

The inertial cavitation (IC) activity of ultrasound contrast agents (UCAs) plays an important role in the development and improvement of ultrasound diagnostic and therapeutic applications. However, various diagnostic and therapeutic applications have different requirements for IC characteristics. Here through IC dose quantifications based on passive cavitation detection, IC thresholds were measured for two commercialized UCAs, albumin-shelled KangRun(®) and lipid-shelled SonoVue(®) microbubbles, at varied UCA volume concentrations (viz., 0.125 and 0.25 vol. %) and acoustic pulse lengths (viz., 5, 10, 20, 50, and 100 cycles). Shell elastic and viscous coefficients of UCAs were estimated by fitting measured acoustic attenuation spectra with Sarkar's model. The influences of sonication condition (viz., acoustic pulse length) and UCA shell properties on IC threshold were discussed based on numerical simulations. Both experimental measurements and numerical simulations indicate that IC thresholds of UCAs decrease with increasing UCA volume concentration and acoustic pulse length. The shell interfacial tension and dilatational viscosity estimated for SonoVue (0.7 ± 0.11 N/m, 6.5 ± 1.01 × 10(-8) kg/s) are smaller than those of KangRun (1.05 ± 0.18 N/m, 1.66 ± 0.38 × 10(-7) kg/s); this might result in lower IC threshold for SonoVue. The current results will be helpful for selecting and utilizing commercialized UCAs for specific clinical applications, while minimizing undesired IC-induced bioeffects.

An experimental system for the study of ultrasound exposure of isolated blood vessels

An experimental system designed for the study of the effects of diagnostic or therapeutic ultrasound exposure on isolated blood vessels in the presence or absence of intraluminal contrast agent is described. The system comprised several components. A microscope was used to monitor vessel size (and thus vessel functionality), and potential leakage of intraluminal 70 kDa FITC-dextran fluorescence marker. A vessel chamber allowed the mounting of an isolated vessel whilst maintaining its viability, with pressure regulation for the control of intraluminal pressure and induction of flow for the infusion of contrast microbubbles. A fibre-optic hydrophone sensor mounted on the vessel chamber using a micromanipulator allowed pre-exposure targeting of the vessel to within 150 µm, and monitoring of acoustic cavitation emissions during exposures. Acoustic cavitation was also detected using changes in the ultrasound drive voltage and by detection of audible emissions using a submerged microphone. The suitability of this system for studying effects in the isolated vessel model has been demonstrated using a pilot study of 6 sham exposed and 18 high intensity focused ultrasound exposed vessels, with or without intraluminal contrast agent (SonoVue) within the vessels.

Therapeutic effects of acoustic cavitation in the presence of gold nanoparticles on a colon tumor model

OBJECTIVES

Acoustic cavitation can be fatal to cells and is used to destroy cancerous tumors. The particles in a liquid decrease the ultrasonic intensity threshold needed for onset of cavitation. Bubble generation from intense pulsed light-irradiated gold nanoparticles was investigated as a means of providing nucleation sites for acoustic cavitation in cancer tissues.

METHODS

This study was conducted on colon carcinoma tumors in BALB/c mice. The tumor-bearing mice were randomly divided into 7 groups (each containing 15 mice): (1) control, (2) gold nanoparticles, (3) intense pulsed light irradiation, (4) intense pulsed light + gold nanoparticles, (5) ultrasound alone, (6) ultrasound + gold nanoparticles, and (7) intense pulsed light + ultrasound + gold nanoparticles. In the respective groups, gold nanoparticles were injected into tumors. Intense pulsed light and ultrasound irradiation were performed on the tumors 24 hours after injection. Antitumor effects were estimated by evaluation of the relative tumor volume, doubling time, and 5-folding time for tumors after treatment. The cumulative survival fraction of the mice and percentage of the lost tissue volume (treated) were also assessed in different groups.

RESULTS

A significant difference in the average relative tumor volumes 15 days after treatment was found between the intense pulsed light + ultrasound + gold nanoparticle group and the other groups (P < .05). The longest doubling and 5-folding times were observed in the intense pulsed light + ultrasound + gold nanoparticles and ultrasound + gold nanoparticle groups.

CONCLUSIONS

Acoustic cavitation in the presence of gold nanoparticles and intense pulsed light has been introduced as a new way for improving therapeutic effects on tumors by reducing the relative tumor volume and increasing the cumulative survival fraction.

Sonochemiluminescence observation of lipid- and polymer-shelled ultrasound contrast agents in 1.2 MHz focused ultrasound field

Ultrasound contrast agents (UCAs) are frequently added into the focused ultrasound field as cavitation nuclei to enhance the therapeutic efficiency. Since their presence will distort the pressure field and make the process unpredictable, comprehension of their behaviors especially the active zone spatial distribution is an important part of better monitoring and using of UCAs. As shell materials can strongly alter the acoustic behavior of UCAs, two different shells coated UCAs, lipid-shelled and polymer-shelled UCAs, in a 1.2 MHz focused ultrasound field were studied by the Sonochemiluminescence (SCL) method and compared. The SCL spatial distribution of lipid-shelled group differed from that of polymer-shelled group. The shell material and the character of focused ultrasound field work together to the SCL distribution, causing the lipid-shelled group to have a maximum SCL intensity in pre-focal region at lower input power than that of polymer-shelled group, and a brighter SCL intensity in post-focal region at high input power. The SCL inactive area of these two groups both increased with the input power. The general behavior of the UCAs can be studied by both the average SCL intensity and the backscatter signals. As polymer-shelled UCAs are more resistant to acoustic pressure, they had a higher destruction power and showed less reactivation than lipid-shelled ones.

Fluorescent microscope system to monitor real-time interactions between focused ultrasound, echogenic drug delivery vehicles, and live cell membranes

Rapid development in the field of ultrasound triggered drug delivery has made it essential to study the real-time interaction between the membranes of live cells and the membranes of echogenic delivery vehicles under exposure to focused ultrasound. The objective of this work was to design an analysis system that combined fluorescent imagining, high speed videography, and definable pulse sequences of focused ultrasound to allow for real time observations of both cell and vehicle membranes. Documenting the behavior of the membranes themselves has not previously been possible due to limitations with existing optical systems used to understand the basic physics of microbubble/ultrasound interaction and the basic interaction between microbubbles and cells. The performance of this new system to monitor membrane behavior was demonstrated by documenting the modes of vehicle fragmentation at different ultrasound intensity levels. At 1.5MPa the membranes were shown to completely fragment while at intensities below 1MPa the membranes pop open and slowly unfold. The interaction between these vehicles and cell membranes was also documented by the removal of fluorescent particles from the surfaces of live cells out to 20μm from the microbubble location. The fluid flow created by microstreaming around ensonated microbubbles was documented at video recording speeds from 60 to 18,000 frames per second. This information about membrane behavior allows the chemical and physical properties of the drug delivery vehicle to be designed along with the ultrasound pulse sequence to cause the most efficient drug delivery.

Phase-change nanoparticles using highly volatile perfluorocarbons: toward a platform for extravascular ultrasound imaging

Recent efforts using perfluorocarbon (PFC) nanoparticles in conjunction with acoustic droplet vaporization has introduced the possibility of expanding the diagnostic and therapeutic capability of ultrasound contrast agents to beyond the vascular space. Our laboratories have developed phase-change nanoparticles (PCNs) from the highly volatile PFCs decafluorobutane (DFB, bp =-2 °C) and octafluoropropane (OFP, bp =-37 °C ) for acoustic droplet vaporization. Studies with commonly used clinical ultrasound scanners have demonstrated the ability to vaporize PCN emulsions with frequencies and mechanical indices that may significantly decrease tissue bioeffects. In addition, these contrast agents can be formulated to be stable at physiological temperatures and the perfluorocarbons can be mixed to modulate the balance between sensitivity to ultrasound and general stability. We herein discuss our recent efforts to develop finely-tuned diagnostic/molecular imaging agents for tissue interrogation. We discuss studies currently under investigation as well as potential diagnostic and therapeutic paradigms that may emerge as a result of formulating PCNs with low boiling point PFCs.

Disruption of splenic circulation using microbubble-enhanced ultrasound and prothrombin: a preliminary study

The spleen is a solid organ in which splenomegaly frequently develops and to which abdominal blunt trauma occurs. In this study, we demonstrated the potential therapeutic effect of microbubble-enhanced ultrasound (MEUS) combined with prothrombin to disrupt splenic circulation. A high-pressure-amplitude therapeutic ultrasound (TUS) device was used to treat 36 surgically exposed spleens in healthy New Zealand rabbits. Eighteen spleens were treated with either MEUS (n = 9) or MEUS combined with prothrombin (n = 9). The other 18 spleens were treated with TUS only or sham ultrasound exposure and served as the controls. The TUS was operated at a frequency of 831 kHz and a peak negative pressure of 4.8 MPa. Prothrombin was administered intravenously at 20 IU/kg. Contrast-enhanced ultrasound (CEUS) and acoustic quantification were performed to assess splenic blood perfusion. We found significant blood perfusion slowdown and drop-off in the MEUS-treated spleens. The peak intensity dropped from 20.2 ± 2.70 dB to 11.6 ± 4.58 dB immediately after treatment. The spleens treated with the combination of MEUS and prothrombin showed consistently poor perfusion within 1 h. In histologic examination of the MEUS-treated spleens, we found significant dilatation of splenic sinuses, hemorrhage, interstitial edema and thrombosis. This study demonstrated that the vascular effects induced by microbubble-enhanced, high-pressure ultrasound can slow down or block blood perfusion in the rabbit spleen. Prothrombin helps to enhance and extend the effects for up to 1 h.

Phase-change contrast agents for imaging and therapy

Phase-change contrast agents (PCCAs) for ultrasound-based applications have resulted in novel ways of approaching diagnostic and therapeutic techniques beyond what is possible with microbubble contrast agents and liquid emulsions. When subjected to sufficient pressures delivered by an ultrasound transducer, stabilized droplets undergo a phase-transition to the gaseous state and a volumetric expansion occurs. This phenomenon, termed acoustic droplet vaporization, has been proposed as a means to address a number of in vivo applications at the microscale and nanoscale. In this review, the history of PCCAs, physical mechanisms involved, and proposed applications are discussed with a summary of studies demonstrated in vivo. Factors that influence the design of PCCAs are discussed, as well as the need for future studies to characterize potential bioeffects for administration in humans and optimization of ultrasound parameters.

Vascular effects of microbubble-enhanced, pulsed, focused ultrasound on liver blood perfusion

The purpose of this study was to investigate the vascular effects of microbubble-enhanced pulsed high-pressure ultrasound on liver blood perfusion. In the presence of circulating lipid-shell microbubbles, a focused ultrasound transducer was used to transcutaneously treat eight livers of healthy rabbits for perfusion analysis and to treat three livers with the abdomen open for histologic analysis. Twenty-two livers treated with the ultrasound only (n = 11) or microbubbles only (n = 11) served as the controls. The focused ultrasound was operated at a frequency of 1.22 MHz with a peak negative pressure of 4.6 MPa. The liver blood perfusion was estimated by performing contrast-enhanced ultrasound and gray-scale quantification on the livers before and after treatment. A temporary, nonenhanced region occurred in all of the experimental livers. The regional contrast gray-scale values of the experimental group dropped significantly from 88.4 before treatment to 2.7 after treatment. The liver perfusion also demonstrated a gradual recovery over a 60-min period. The liver perfusion of the control groups remained the same after treatment. We found microvascular rupture, hemorrhage and swelling hepatocytes upon histologic examination of the experimental group. Regional liver blood perfusion can be temporarily blocked by microbubble-enhanced focused ultrasound with high-pressure amplitude. These vascular effects can be explained as acute microvascular injury of the liver and may have clinical implications.

In vivo gene transfer into the ocular ciliary muscle mediated by ultrasound and microbubbles

This study aimed to assess application of ultrasound (US) combined with microbubbles (MB) to transfect the ciliary muscle of rat eyes. Reporter DNA plasmids encoding for Gaussia luciferase, β-galactosidase or the green fluorescent protein (GFP), alone or mixed with 50% Artison MB, were injected into the ciliary muscle, with or without US exposure (US set at 1 MHz, 2 W/cm(2), 50% duty cycle for 2 min). Luciferase activity was measured in ocular fluids at 7 and 30 days after sonoporation. At 1 week, the US+MB treatment showed a significant increase in luminescence compared with control eyes, injected with plasmid only, with or without MB (×2.6), and, reporter proteins were localized in the ciliary muscle by histochemical analysis. At 1 month, a significant decrease in luciferase activity was observed in all groups. A rise in lens and ciliary muscle temperature was measured during the procedure but did not result in any observable or microscopic damages at 1 and 8 days. The feasibility to transfer gene into the ciliary muscle by US and MB suggests that sonoporation may allow intraocular production of proteins for the treatment of inflammatory, angiogenic and/or degenerative retinal diseases.

Modeling cavitation nucleation from laser-illuminated nanoparticles subjected to acoustic stress

In an earlier work by Farny et al. [ARLO 6, 138-143 (2005).] it was demonstrated that the acoustic cavitation threshold in a tissue mimicking gel phantom can be lowered from 4.5 to ∼1 MPa by "seeding" the optically transparent phantom with light absorptive gold nanoparticles and irradiating these absorbers with nanosecond pulses of laser light at intensities less than 10 mJ/cm(2). As a follow-up study, a three-stage numerical model was developed to account for prenucleation heating, the nucleation and formation of the vapor cavity, and the resulting vapor bubble dynamics. Through examination of the radius-time evolution of the cavity, the combined thresholds for laser radiant exposure and acoustic peak pressure required to induce inertial cavitation are deduced. It is found that the threshold pressure decreases when laser exposure increases; but the rate depends on exposure levels and the size of the particle. Investigations of the roles of particle size and laser pulse length are performed and optimum choices for these parameters determined in order to obtain inertial cavitation at the lowest possible acoustic pressure and laser intensity.

The influence of octyl β-D-glucopyranoside on cell lysis induced by ultrasonic cavitation

Octyl β-D-glucopyranoside (OGP) has been reported to completely inhibit cavitation-induced cell lysis in vitro, possibly by quenching critical free-radical effects. In this study, the influence of OGP on cell lysis in a 60 rpm rotating-tube exposure apparatus was assessed. HL-60 cell lysis was estimated with a Coulter Multisizer counter. Cavitation activity from the 2.3 MHz, 30 s duration exposures were monitored at the 1.15 MHz subharmonic. Cavitation nucleation was accomplished by addition of an ultrasound contrast agent, or by using freshly dissolved culture media. For both nucleation methods, exposures were conducted for 0-0.7 MPa peak rarefactional pressure-amplitudes with and without 5 mM OGP, and for 0.5 MPa with 0-5 mM OGP. The addition of OGP to the cell suspension medium generally had little influence on cavitation-induced cell lysis. Exposures with no rotation had reduced subharmonic and lysis for added contrast agent, but essentially no cavitation for the fresh medium. Since the decreases or increases in cell lysis found for added OGP generally were accounted for by concomitant decreases or increases in cavitation activity, the changes in cell lysis could be explained by variation of the mechanical effects of cavitation without invoking a critical role for free-radical effects.

Enhancement of vancomycin activity against biofilms by using ultrasound-targeted microbubble destruction

Treating biofilm infections on implanted medical devices is formidable, even with extensive antibiotic therapy. The aim of this study was to investigate whether ultrasound (US)-targeted microbubble (MB) destruction (UTMD) could enhance vancomycin activity against Staphylococcus epidermidis RP62A biofilms. Twelve-hour biofilms were treated with vancomycin combined with UTMD. The vancomycin and MB (SonoVue) were used at concentrations of 100 μg/ml and 30% (vol/vol), respectively, in studies in vitro. After US exposure (0.08 MHz, 1.0 W/cm(2), 50% duty cycle, and 10-min duration), the biofilms were cultured at 37 °C for another 12 h. The results showed that many micropores were found in biofilms treated with vancomycin combined with UTMD. Biofilm densities (A(570) values) and the viable counts of S. epidermidis recovered from the biofilm were significantly decreased compared with those of any other groups. Furthermore, the highest percentage of dead cells was found, using confocal laser scanning microscopy, in the biofilm treated with vancomycin combined with UTMD. The viable counts of bacteria in biofilms in an in vivo rabbit model also confirmed the enhanced effect of vancomycin combined with UTMD. UTMD may have great potential for improving antibiotic activity against biofilm infections.

Role of constituents of Optison in Optison-mediated gene transfection enhancement in skeletal muscle in vivo

OBJECTIVES

The mechanism by which Optison (an albumin-shelled, octafluoropropane gas-filled microbubble contrast agent; Amersham Health, Amersham, England) enhances gene transfection in skeletal muscle in vivo with or without ultrasound (US) is unclear. The possible mechanisms were investigated by experimenting with different constituents, both with and without US.

METHODS

Plasmid DNA (10 μg) encoding green fluorescent protein was mixed with Optison or its constituents dissolved in saline (in an equivalent concentration as in Optison) and injected into the tibialis anterior muscle of mice with or without adjunct US (1 MHz, 2 W/cm², 30 seconds, and 20% duty cycle). The efficiencies of green fluorescent protein transgene expression were determined under different experimental conditions: (1) plasmid plus saline as a negative control; (2) plasmid plus Optison as a positive control; (3) plasmid plus heat-treated Optison (without microbubbles); (4) plasmid plus human serum albumin; (5) plasmid plus N-acetyltryptophan; and (6) plasmid plus caprylic acid. Transfection efficiency was assessed by counting the maximum number of green fluorescent protein-positive fibers. Tissue damage was assessed by measuring the damaged area on serial sections.

RESULTS

Heat-treated Optison with or without US and albumin with US showed similarly high levels of transgene expression as Optison in mouse muscle without substantially increased tissue damage. N-Acetyltryptophan and caprylic acid had no effect on the delivery of plasmid green fluorescent protein into mouse muscle but instead showed the potential to increase tissue damage.

CONCLUSIONS

These data suggest that US and albumin separately potentiate transfection in this model. The combination of albumin and perfluoropropane is highly effective, which probably explains why Optison is so effective.

In vitro characterization of perfluorocarbon droplets for focused ultrasound therapy

Focused ultrasound therapy can be enhanced with microbubbles by thermal and cavitation effects. However, localization of treatment is difficult as bioeffects can occur outside of the target region. Spatial control of bubbles can be achieved by ultrasound-induced conversion of liquid perfluorocarbon droplets to gas bubbles. This study was undertaken to determine the acoustic parameters for bubble production by droplet conversion and how it depends on the acoustic conditions and droplet physical parameters. Lipid-encapsulated droplets containing dodecafluoropentane were manufactured with sizes ranging from 1.9 to 7.2 microm in diameter and diluted to a concentration of 8 x 10(6) droplets mL(-1). The droplets were sonicated in vitro with a focused ultrasound transducer and varying frequency and exposure under flow conditions through an acoustically transparent vessel. The sonications were 10 ms in duration at frequencies of 0.578, 1.736 and 2.855 MHz. The pressure threshold for droplet conversion was measured with an active transducer operating in pulse-echo mode and simultaneous measurements of broadband acoustic emissions were performed with passive acoustic detection. The results show that droplets cannot be converted at low frequency without broadband emissions occurring. However, the pressure threshold for droplet conversion decreased with increasing frequency, exposure and droplet size. The pressure threshold for broadband emissions was independent of the droplet size and was 2.9, 4.4 and 5.3 MPa for 0.578, 1736 and 2.855 MHz, respectively. In summary, we have demonstrated that droplet conversion is feasible for clinically relevant sized droplets and acoustic exposures.

High-intensity focused ultrasound induced apoptosis with caspase 3, 8, and 9/6 activation in rat hepatoma

PURPOSE

The purpose of the present study is to investigate anticancer efficacy and apoptosis confirmed by caspase under several exposure conditions of high-intensity focused ultrasound (HIFU).

MATERIALS AND METHODS

Twenty-five rats with KDH-8 hepatoma were treated by HIFU at several acoustic energies to evaluate treatment efficacy. Apoptosis was examined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and Hoechst 33258 staining, and caspase 3, 8, and 9/6 activity was respectively assayed.

RESULTS

The KDH-8 subcutaneous tumors were reduced by HIFU, and these rats survived longer than the nontreatment rats (P < 0.01). The minimal threshold of HIFU energy was 30 W × 1.0 s for tumor control and long-term survival. The tumors exposed to HIFU exhibited marked apoptotic features under conditions of less than 10 W × 1.0 s. In cultured KDH-8 cells, apoptosis was caused at less than 30 W × 1.0 s (P < 0.01), and more was induced as the energy went down. Caspase 3, 8, and 9/6 were more activated at low energy under 10 W × 1.0 s (P < 0.01), and caspase 8, which is death receptor dependent, was significantly more activated than caspase 9/6, which is mitochondria dependent (P < 0.01).

CONCLUSION

HIFU-induced apoptosis in vivo and in vitro is one of the mechanisms for tumor control and is mediated by caspase 3, 8, and 9/6. The significantly greater activation of caspase 8 than of caspase 9/6 suggests that the apoptosis pathway induced by HIFU might be more mitochondria dependent than death receptor dependent. However, further examination will be needed.

An ex vivo study of the correlation between acoustic emission and microvascular damage

The objective of this study was to conduct an ex vivo examination of correlation between acoustic emission and tissue damage. Intravital microscopy was employed in conjunction with ultrasound exposure in cremaster muscle of male Wistar rats. Definity microbubbles were administered intravenously through the tail vein (80microL.kg(-1).min(-1)infusion rate) with the aid of a syringe pump. For the pulse repetition frequency (PRF) study, exposures were performed at four locations of the cremaster at a PRF of 1000, 500, 100 and 10Hz (one location per PRF per rat). The 100-pulse exposures were implemented at a peak rarefactional pressure (P(r)) of 2MPa, frequency of 2.25MHz with 46 cycle pulses. For the pressure amplitude threshold study, 100-pulse exposures (46 cycle pulses) were conducted at various peak rarefactional pressures from 0.5MPa to 2MPa at a frequency of 2.25MHz and PRF of 100Hz. Photomicrographs were captured before and 2-min postexposure. On a pulse-to-pulse basis, the 10Hz acoustic emission was considerably higher and more sustained than those at other PRFs (1000, 500, and 100Hz) (p<0.05). Damage, measured as area of extravasation of red blood cells (RBCs), was also significantly higher at 10Hz PRF than at 1000, 500 and 100Hz (p<0.01). The correlation of acoustic emission to tissue damage showed a trend of increasing damage with increasing cumulative function of the relative integrated power spectrum (CRIPS; R(2)=0.75). No visible damage was present at P(r)< or =0.85MPa. Damage, however, was observed at P(r)> or =1.0MPa and it increased with increasing acoustic pressure.

In vivo gas body efficacy for glomerular capillary hemorrhage induced by diagnostic ultrasound in rats

Glomerular capillary hemorrhage (GCH) in rat kidney provided a model for assessing in vivo gas body efficacy in diagnostic or therapeutic applications of ultrasound. Two diagnostic ultrasound machines were utilized: one monitored the harmonic B-mode contrast enhancement of the left kidney and the other exposed the right kidney for GCH production. Definity contrast agent was infused at 1, 2, 5, or 10 microL/(kg x min) and infusion durations were 30, 60, 120, or 300 s. Exposure of the right kidney was at a peak rarefactional pressure amplitude of 2.3 MPa at 1.5 MHz. The circulating dose was estimated with a simple model of agent dilution and gas body loss. For 300 s infusion at 5 microL/(kg x min), the left kidney image brightness increased to a plateau with an estimated 6.4 +/- 1.3 microL/kg circulating dose with no GCH in histological sections. Exposure of the right kidney with a 1-s image interval reduced the estimated circulating dose to 1.3 +/- 0.3 microL/kg and induced 68.4% GCH. Dose and duration increases gave rapidly diminishing treatment effectiveness per gas body. The effective in vivo agent dose in rats can be reduced greatly due to high gas body destruction in the small animal, complicating predictions for similar conditions of human treatment.