Ultrasound enhancement of liposome-mediated cell transfection is caused by cavitation effects

Facilitating New Chromium Reducing Microbes to Enhance Hexavalent Chromium Reduction by In Situ Sonoporation-Mediated Gene Transfer in Soils

Chromium (Cr) is a heavy metal with a high toxicity and pathogenicity. Microbial reduction is an effective strategy to remove Cr(VI) at contaminated sites but suffers from the low populations and activities of Cr-reducing microorganisms in soils. This study proposed an in situ sonoporation-mediated gene transfer approach, which improved soil Cr(VI) reduction performance by delivering exogenous Cr-transporter chrA genes and Cr-reducing yieF genes into soil microorganisms with the aid of ultrasound. Besides the increasing populations of Cr-resistant bacteria and elevated copy numbers of chrA and yieF genes after sonoporation-mediated gene transfer, three new Cr-reducing strains were isolated, among which Comamonas aquatica was confirmed to obtain Cr-resistant capability. In addition, sonoporation-mediated gene transfer was the main driving force significantly shaping soil microbial communities owing to the predominance of Cr-resistant microbes. This study pioneered and evidenced that in situ soil sonoporation-mediated gene transfer could effectively deliver functional genes into soil indigenous microbes to facilitate microbial functions for enhanced bioremediation, e.g., Cr-reduction in this study, showing its feasibility as a chemically green and sustainable remediation strategy for heavy metal contaminated sites.

Recent advances in ultrasound-triggered drug delivery through lipid-based nanomaterials

The high prescribed dose of anticancer drugs and their resulting adverse effects on healthy tissue are significant drawbacks to conventional chemotherapy (CTP). Ideally, drugs should have the lowest possible degree of interaction with healthy cells, which would diminish any adverse effects. Therefore, an ideal scenario to bring about improvements in CTP is the use of technological strategies to ensure the efficient, specific, and selective transport and/or release of drugs to the target site. One practical and feasible solution to promote the efficiency of conventional CTP is the use of ultrasound (US). In this review, we highlight the potential role of US in combination with lipid-based carriers to achieve a targeted CTP strategy in engineered smart drug delivery systems.

Enhancing Nucleic Acid Delivery with Ultrasound and Microbubbles

For gene therapy to work in vivo, nucleic acids need to reach the target cells without causing major side effects to the patient. In many cases the gene only has to reach a subset of cells in the body. Therefore, targeted delivery of genes to the desired tissue is a major issue in gene delivery. Many different possibilities of targeted gene delivery have been studied. A physical approach to target nucleic acids and other drugs to specific regions in the body is the use of ultrasound and microbubbles. Microbubbles are gas filled spheres with a stabilizing lipid, protein, or polymer shell. When these microbubbles enter an ultrasonic field, they start to oscillate. The bubbles' expansion and compression are inversely related to the pressure phases in the ultrasonic field. When microbubbles are exposed to high-intensity ultrasound the microbubbles will eventually implode and fragment. This generates shockwaves and microjets which can temporarily permeate cell membranes and blood vessels. Nucleic acids or (non)viral vectors can as a result gain direct access to either the cytoplasm of neighboring cells, or extravasate to the surrounding tissue. The nucleic acids can either be mixed with the microbubbles or loaded on the microbubbles. Nucleic acid loaded microbubbles can be obtained by coupling nucleic acid-containing particles (i.e., lipoplexes) to the microbubbles. Upon ultrasound-mediated implosion of the microbubbles, the nucleic acid-containing particles will be released and will deliver their nucleic acids in the ultrasound-targeted region.

State-of-the-art of microbubble-assisted blood-brain barrier disruption

Focused ultrasound with microbubbles promises unprecedented advantages for blood-brain barrier disruption over existing intracranial drug delivery methods, as well as a significant number of tunable parameters that affect its safety and efficacy. This review provides an engineering perspective on the state-of-the-art of the technology, considering the mechanism of action, effects of microbubble properties, ultrasound parameters and physiological variables, as well as safety and potential therapeutic applications. Emphasis is placed on the use of unified parameters, such as microbubble volume dose (MVD) and ultrasound mechanical index, to optimize the procedure and establish safety limits. It is concluded that, while efficacy has been demonstrated in several animal models with a wide range of payloads, acceptable measures of safety should be adopted to accelerate collaboration and improve understanding and clinical relevance.

Ultrasound Contrast Agents and Delivery Systems in Cancer Detection and Therapy

Ultrasound is the second most utilized imaging modality in the world because it is widely accessible, robust, and safe. Aside from its extensive use in diagnostic imaging, ultrasound has also been frequently utilized in therapeutic applications. Particularly, when combined with appropriate delivery systems, ultrasound provides a flexible platform for simultaneous real-time imaging and triggered release, enabling precise, on-demand drug delivery to target sites. This chapter will discuss the basics of ultrasound including its mechanism of action and how it can be used to trigger the release of encapsulated drug either through thermal or cavitation effects. Fundamentals of ultrasound contrast agents, how they enhance ultrasound signals, and how they can be modified to function as carriers for triggered and targeted release of drugs will also be discussed.

Shock wave-induced permeabilization of mammalian cells

Controlled permeabilization of mammalian cell membranes is fundamental to develop gene and cell therapies based on macromolecular cargo delivery, a process that emerged against an increasing number of health afflictions, including genetic disorders, cancer and infections. Viral vectors have been successfully used for macromolecular delivery; however, they may have unpredictable side effects and have been limited to life-threatening cases. Thus, several chemical and physical methods have been explored to introduce drugs, vaccines, and nucleic acids into cells. One of the most appealing physical methods to deliver genes into cells is shock wave-induced poration. High-speed microjets of fluid, emitted due to the collapse of microbubbles after shock wave passage, represent the most significant mechanism that contributes to cell membrane poration by this technique. Herein, progress in shock wave-induced permeabilization of mammalian cells is presented. After covering the main concepts related to molecular strategies whose applications depend on safer drug delivery methods, the physics behind shock wave phenomena is described. Insights into the use of shock waves for cell membrane permeation are discussed, along with an overview of the two major biomedical applications thereof-i.e., genetic modification and anti-cancer shock wave-assisted chemotherapy. The aim of this review is to summarize 30 years of data showing underwater shock waves as a safe, noninvasive method for macromolecular delivery into mammalian cells, encouraging the development of further research, which is still required before the introduction of this promising tool into clinical practice.

Sonoluminescence and acoustic emission spectra at different stages of cavitation zone development

The way in which a cavitation zone develops in a focused pulsed ultrasound field is studied in this work. Sonoluminescence (SL), total hydrophone output and cavitation noise spectra have been recorded across a gradual, smooth increase in applied voltage. It is shown that the cavitation zone passes through a number of stages of evolution, according to increasing ultrasound intensity, decreasing pulse period and increasing ultrasound pulse duration. Sonoluminescence is absent in the first phase and the hydrophone output spectra consists of a main line with two or three harmonics whose intensity is much lower than that of the main (fundamental) line. The second stage sees the onset of SL whose intensity increases smoothly and is accompanied by the appearance of higher harmonics and subharmonics in the cavitation noise spectra. In some cases, the wide-band (WBN) component can be seen in noise spectra during the final part of the second stage. In the third stage, SL intensity increases significantly and often quite sharply, while WBN intensity increases in the same manner. This is accompanied by a synchronous increase in the absorption of ultrasound by the cavitation zone, which is manifested in a sharp decrease in the hydrophone output. In the fourth stage, both SL and WBN intensities tend to decrease despite the increased voltage applied to the transducer. Furthermore, the fundamental line tends to decrease in strength as well, despite the increasing ultrasound intensity. The obtained results clearly identify the different stages of cavitation zone development using cavitation noise spectra analyses. We then hypothesize that three of the above stages may be responsible for three known types of ultrasound action on biological cells: damping viability, reversible cell damage (sonoporation) and irreversible damage/cytotoxicity.

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.

FRET-based method for evaluation of the efficiency of reversible and irreversible sonoporation

It is widely known that not all of the treated cells survive after introduction of exogenous molecules via any physical method. Therefore, it is important to develop methods that would allow simultaneous evaluation of both molecular delivery efficiency and cell viability. This study presents Förster resonance energy transfer (FRET)-based method that allows molecular transfer and cell viability evaluation in a single measurement by employing two common fluorescent dyes, namely, ethidium bromide and trypan blue. The method has been validated using cell sonoporation. The FRET-based method allows the efficiency evaluation of both reversible and irreversible sonoporation in a single experiment. Therefore, this method could be used to reduce time, labor, and material cost while improving the accuracy of evaluations.

[Research of enhanced green fluorescent protein gene transfer with ultrasound-mediated microbubble destruction in bone defects]

Objective

To investigate the effect of ultrasonic irradiation time on enhanced green fluorescent protein (EGFP) gene transfection efficiency and local tissue in bone defects using ultrasound-mediated microbubble destruction.

Methods

Thirty 3-month-old New Zealand rabbits (2.5-3.0 kg in weight) were randomly divided into 5 groups ( n=6) and bone defect models were made on the right ulna. At 10 days after modeling, suspension of microbubbles and EGFP plasmids were locally injected (0.3 mL/kg) and then ultrasound was performed on defect at a frequency of 1 MHz, a intensity of 0.5 W/cm 2, and a duty ratio of 20% for 1, 2, 3, 4, and 5 minutes respectively (in 1, 2, 3, 4, and 5 minutes groups respectively). The survival condition was observed. Rabbits were sacrificed for gross observation at 7 days after transfer. The gene expression was observed by fluorescence staining. HE staining and transmission electron microscopy were used to observe the local tissue damage.

Results

The animals all survived. New soft tissue formed in bone defects area at 1 week after transfer, the surrounding muscle tissue was partly filled in it. Green fluorescence expression was observed in all rabbits. The expression was the strongest in 2 minutes group, and was the weakest in 1 minute group. The absorbance ( A) value showed significant differences when compared 1 minute and 2 minutes groups with other groups ( P<0.05), but no significant difference was found between 3, 4, and 5 minutes groups ( P>0.05). Tissue damage was observed in all groups and it was aggravated with the increase of irradiation time.

Conclusion

EGFP transfection efficiency in bone defect by ultrasound-mediated microbubble destruction is related to irradiation time. EGFP gene can be efficiently transfected without obvious toxicity at 1 MHz, 0.5W/cm 2, and duty ratio of 20% for 2 minutes in bone defects of rabbits.

Numerical study of a confocal ultrasonic setup for cavitation creation

Acoustic cavitation has found a wide range of applications in the last few decades. For potential applications involving cavitation, the acoustic characteristics of a confocal ultrasonic setup are studied: two high-intensity focused ultrasound transducers are mounted so that their focal points overlap. A mathematical simulator is developed that takes into account nonlinear propagation, absorption, and diffraction. Each one of these physical effects is solved in the frequency domain for successive planes. Comparing the confocal setup with equivalent single transducer setups, it is shown that, with the confocal configuration, nonlinear distortion of the waveform is reduced, resulting in a greater peak rarefactional pressure and a lower peak positive pressure. Furthermore, additional features are investigated for confocal configurations such as a greater spatial stability for the focal point, which can be maintained while increasing the pressure level, and a focal region consisting of interference acting as an acoustic trap.

Measuring cavitation and its cleaning effect

The advantages and limitations of techniques for measuring the presence and amount of cavitation, and for quantifying the removal of contaminants, are provided. After reviewing chemical, physical, and biological studies, a universal cause for the cleaning effects of bubbles cannot yet be concluded. An "ideal sensor" with high spatial and temporal resolution is proposed. Such sensor could be used to investigate bubble jetting, shockwaves, streaming, and even chemical effects, by correlating cleaning processes with cavitation effects, generated by hydrodynamics, lasers or ultrasound.

Nanoethosomal transdermal delivery of vardenafil for treatment of erectile dysfunction: optimization, characterization, and in vivo evaluation

Vesicular drug delivery systems have recently gained attention as a way of improving dosing accuracy for drugs with poor transdermal permeation. The current study focuses on utilization of the natural biocompatible vesicles to formulate vardenafil nanoethosomes (VRD-NE), for the enhancement of their transdermal permeation and bioavailability. Fifteen formulations were prepared by thin-layer evaporation technique according to Box–Behnken design to optimize formulation variables. The effects of lipid composition, sonication time, and ethanol concentration on particle size and encapsulation efficiency were studied. The diffusion of vardenafil (VRD) from the prepared nanoethosomes specified by the design was carried out using automated Franz diffusion cell apparatus. The optimized formula was investigated for in vivo pharmacokinetic parameters compared with oral VRD suspension. Confocal laser scanning microscopy images were used to confirm enhanced diffusion release of VRD in rat skin. The results showed that the optimized formula produced nanoethosomes with an average size of 128 nm and an entrapment efficiency of 76.23%. VRD-NE provided a significant improvement in permeation with an enhancement ratio of 3.05-fold for a film made with optimally formulated VRD-NE compared with a film made with VRD powder. The transdermal bioavailability of VRD from the nanoethosome film was approximately twofold higher than the oral bioavailability from an aqueous suspension. VRD-NE thus provide a promising transdermal drug delivery system. As a result, management of impotence for a longer duration could be achieved with a reduced dosage rate that improves patient tolerability and compliance for the treatment of erectile dysfunction.

Improvement of fluvastatin bioavailability by loading on nanostructured lipid carriers

The aim of this study is to prepare fluvastatin nanostructured lipid carriers (FLV-NLCs) in order to find an innovative way to alleviate FLV-associated disadvantages. The limitations include poor solubility and extensive first-pass metabolism, resulting in low (30%) bioavailability and short elimination half-life (1–3 hours). FLV-NLCs were prepared by hot emulsification–ultrasonication method. Ten runs were created by three-level factorial design (32) to optimize FLV-NLCs formulation process. In this study, two factors, four responses, and three-level factorial design were endorsed. The studied variables were lipid:oil ratio (X₁) and sonication time (X₂). However, the responses parameter determined the particle size (Y₁, nm), entrapment efficiency percent (EE%, Y₂), particles zeta potential (Y₃), and 80% of the drug release after 24 hours (X₄). Furthermore, stability and in vivo pharmacokinetics were studied in rats. The optimized consisted formula had an average particle size of 165 nm with 75.32% entrapment efficiency and 85.32% of drug released after 24 hours, demonstrating a sustaining drug release over 24 hours. An in vivo pharmacokinetic study revealed enhanced bioavailability by >2.64-fold, and the mean residence time was longer than that of FLV. We concluded that NLCs could be promising carriers for sustained/prolonged FLV release with enhanced oral bioavailability.

Cytosolic delivery via escape from the endosome using emulsion droplets and ultrasound

Vaporizing emulsion droplets may aid in endosomal rupture as a drug delivery route to the cytosol. Upon insonation, emulsion droplets formed from perfluorocarbon liquids may vaporize with sufficient expansion to disrupt liposomal or endosomal membranes. Emulsion droplets of perfluorohexane (PFC6) or perfluoropentane (PFC5) were prepared as free droplets in calcein or as droplets encapsulated within liposomes containing calcein. Folate-stimulated endocytosis created an experimental model, wherein calcein was self-quenched until released from the vesicles. Upon release, calcein was diluted below its self-quenching concentration and its release quantified by fluorescence. In this experimental model, folated emulsions or folated eLiposomes were incubated with folate-starved HeLa cells. Samples were exposed to two seconds of 20-kHz ultrasound (US) at 1 W/cm(2). Fluorescence microscopy identified released intracellular calcein. Upon insonation, both free emulsion samples and eLiposome samples produced calcein release to the cytosol. Calcein fluorescence was more intense in samples containing PFC5 compared to PFC6. Insonation of samples without emulsion droplets produced no cytosolic delivery. Likewise, cells that took up emulsion droplets but were not exposed to US did not exhibit fluorescence throughout the cell. These results suggest that vaporizing emulsion droplets are internalized into the cells and can produce endosomal escape of a therapeutic payload.

Improve bio-activity of anaerobic sludge by low energy ultrasound

This research focused on ultrasound-enhanced bio-activity of anaerobic sludge. Low energy ultrasound irradiation can increase the bio-activity of anaerobic sludge. Ultrasonic parameter, characteristics of anaerobic sludge and experimental conditions are important parameters which affect the enhancement effect on anaerobic sludge. In order to assess the effects of characteristics of anaerobic sludge and experimental conditions on ultrasonic irradiation of anaerobic sludge, experiments with different characteristics of anaerobic sludge were carried out and analyzed with the content of coenzyme F420 and dehydrogenase activity (DHA). The results showed that anaerobic sludge bio-activity was impacted by the initial temperature, initial chemical oxygen demand (COD), sludge concentration, and stirring during the ultrasonic process. Optimal performance was achieved when sound frequency, power density, and ultrasonic irradiation period was 20 kHz, 0.1 W/mL, and 10 min, respectively, under which the wastewater COD removal efficiency was increased by 12.9 percentage points. The results indicated that low temperature could affect the anaerobic sludge irradiation effect, while intermittent stirring could enhance the bio-activity of anaerobic sludge irradiation effect and low substrate concentration improved anaerobic sludge activity by ultrasound.

Effects of microbubble size on ultrasound-mediated gene transfection in auditory cells

Gene therapy for sensorineural hearing loss has recently been used to insert genes encoding functional proteins to preserve, protect, or even regenerate hair cells in the inner ear. Our previous study demonstrated a microbubble- (MB-)facilitated ultrasound (US) technique for delivering therapeutic medication to the inner ear. The present study investigated whether MB-US techniques help to enhance the efficiency of gene transfection by means of cationic liposomes on HEI-OC1 auditory cells and whether MBs of different sizes affect such efficiency. Our results demonstrated that the size of MBs was proportional to the concentration of albumin or dextrose. At a constant US power density, using 0.66, 1.32, and 2.83 μm albumin-shelled MBs increased the transfection rate as compared to the control by 30.6%, 54.1%, and 84.7%, respectively; likewise, using 1.39, 2.12, and 3.47 μm albumin-dextrose-shelled MBs increased the transfection rates by 15.9%, 34.3%, and 82.7%, respectively. The results indicate that MB-US is an effective technique to facilitate gene transfer on auditory cells in vitro. Such size-dependent MB oscillation behavior in the presence of US plays a role in enhancing gene transfer, and by manipulating the concentration of albumin or dextrose, MBs of different sizes can be produced.

Ultrasound-mediated local drug and gene delivery using nanocarriers

With the development of nanotechnology, nanocarriers have been increasingly used for curative drug/gene delivery. Various nanocarriers are being introduced and assessed, such as polymer nanoparticles, liposomes, and micelles. As a novel theranostic system, nanocarriers hold great promise for ultrasound molecular imaging, targeted drug/gene delivery, and therapy. Nanocarriers, with the properties of smaller particle size, and long circulation time, would be advantageous in diagnostic and therapeutic applications. Nanocarriers can pass through blood capillary walls and cell membrane walls to deliver drugs. The mechanisms of interaction between ultrasound and nanocarriers are not clearly understood, which may be related to cavitation, mechanical effects, thermal effects, and so forth. These effects may induce transient membrane permeabilization (sonoporation) on a single cell level, cell death, and disruption of tissue structure, ensuring noninvasive, targeted, and efficient drug/gene delivery and therapy. The system has been used in various tissues and organs (in vitro or in vivo), including tumor tissues, kidney, cardiac, skeletal muscle, and vascular smooth muscle. In this review, we explore the research progress and application of ultrasound-mediated local drug/gene delivery with nanocarriers.

Permeabilization of adhered cells using an inert gas jet

Various cell transfection techniques exist and these can be broken down to three broad categories: viral, chemical and mechanical. This protocol describes a mechanical method to temporally permeabilize adherent cells using an inert gas jet that can facilitate the transfer of normally non-permeable macromolecules into cells. We believe this technique works by imparting shear forces on the plasma membrane of adherent cells, resulting in the temporary formation of micropores. Once these pores are created, the cells are then permeable to genetic material and other biomolecules. The mechanical forces involved do run the risk of permanently damaging or detaching cells from their substrate. There is, therefore, a narrow range of inert gas dynamics where the technique is effective. An inert gas jet has proven efficient at permeabilizing various adherent cell lines including HeLa, HEK293 and human abdominal aortic endothelial cells. This protocol is appropriate for the permeabilization of adherent cells both in vitro and, as we have demonstrated, in vivo, showing it may be used for research and potentially in future clinical applications. It also has the advantage of permeabilizing cells in a spatially restrictive manner, which could prove to be a valuable research tool.

Microfluidic electro-sonoporation: a multi-modal cell poration methodology through simultaneous application of electric field and ultrasonic wave

A microfluidic device that simultaneously applies the conditions required for microelectroporation and microsonoporation in a flow-through scheme toward high-efficiency and high-throughput molecular delivery into mammalian cells is presented. This multi-modal poration microdevice using simultaneous application of electric field and ultrasonic wave was realized by a three-dimensional (3D) microelectrode scheme where the electrodes function as both electroporation electrodes and cell flow channel so that acoustic wave can be applied perpendicular to the electric field simultaneously to cells flowing through the microfluidic channel. This 3D microelectrode configuration also allows a uniform electric field to be applied while making the device compatible with fluorescent microscopy. It is hypothesized that the simultaneous application of two different fields (electric field and acoustic wave) in perpendicular directions allows formation of transient pores along two axes of the cell membrane at reduced poration intensities, hence maximizing the delivery efficiency while minimizing cell death. The microfluidic electro-sonoporation system was characterized by delivering small molecules into mammalian cells, and showed average poration efficiency of 95.6% and cell viability of 97.3%. This proof of concept result shows that by combining electroporation and sonoporation together, significant improvement in molecule delivery efficiency could be achieved while maintaining high cell viability compared to electroporation or sonoporation alone. The microfluidic electro-sonoporation device presented here is, to the best of our knowledge, the first multi-modal cell poration device using simultaneous application of electric field and ultrasonic wave. This new multi-modal cell poration strategy and system is expected to have broad applications in delivery of small molecule therapeutics and ultimately in large molecule delivery such as gene transfection applications where high delivery efficiency and high viability are crucial.

Microbubble-mediated ultrasound therapy: a review of its potential in cancer treatment

The inherently toxic nature of chemotherapy drugs is essential for them to kill cancer cells but is also the source of the detrimental side effects experienced by patients. One strategy to reduce these side effects is to limit the healthy tissue exposure by encapsulating the drugs in a vehicle that demonstrates a very low leak rate in circulation while simultaneously having the potential for rapid release once inside the tumor. Designing a vehicle with these two opposing properties is the major challenge in the field of drug delivery. A triggering event is required to change the vehicle from its stable circulating state to its unstable release state. A unique mechanical actuation type trigger is possible by harnessing the size changes that occur when microbubbles interact with ultrasound. These mechanical actuations can burst liposomes and cell membranes alike allowing for rapid drug release and facilitating delivery into nearby cells. The tight focusing ability of the ultrasound to just a few cubic millimeters allows for precise control over the tissue location where the microbubbles destabilize the vehicles. This allows the ultrasound to highlight the tumor tissue and cause rapid drug release from any carrier present. Different vehicle designs have been demonstrated from carrying drug on just the surface of the microbubble itself to encapsulating the microbubble along with the drug within a liposome. In the future, nanoparticles may extend the circulation half-life of these ultrasound triggerable drug-delivery vehicles by acting as nucleation sites of ultrasound-induced mechanical actuation. In addition to the drug delivery capability, the microbubble size changes can also be used to create imaging contrast agents that could allow the internal chemical environment of a tumor to be studied to help improve the diagnosis and detection of cancer. The ability to attain truly tumor-specific release from circulating drug-delivery vehicles is an exciting future prospect to reduce chemotherapy side effects while increasing drug effectiveness.

Enhancing nucleic acid delivery with ultrasound and microbubbles

For gene therapy to work in vivo, nucleic acids need to reach the target cells without causing major side effects to the patient. In many cases the gene only has to reach a subset of cells in the body. Therefore, targeted delivery of genes to the desired tissue is a major issue in gene delivery. Many different possibilities of targeted gene delivery have been studied. A relatively novel approach to target nucleic acids and other drugs to specific regions in the body is the use of ultrasound and microbubbles. Microbubbles are gas-filled spheres with a stabilizing lipid, protein, or polymer shell. When these microbubbles enter an ultrasonic field, they start to oscillate. The bubble expansion and compression are inversely related to the pressure phases in the ultrasonic field. When microbubbles are exposed to high-intensity ultrasound they will eventually implode and fragment. This generates shockwaves and microjets which can temporarily permeate cell membranes and blood vessels. Nucleic acids or (non)-viral vectors can extravasate through these pores to gain access to the cell's cytoplasm or the surrounding tissue. The nucleic acids can either be mixed with the microbubbles or loaded on the microbubbles. Nucleic acid-loaded microbubbles can be obtained by coupling nucleic acid-containing particles (i.e., lipoplexes) to the microbubbles. Upon ultrasound-mediated implosion of the microbubbles, the nucleic acid-containing particles will be released and will deliver their nucleic acids in the ultrasound-targeted region.

Use of inert gas jets to measure the forces required for mechanical gene transfection

Background

Transferring genes and drugs into cells is central to how we now study, identify and treat diseases. Several non-viral gene therapy methods that rely on the mechanical disruption of the plasma membrane have been proposed, but the success of these methods has been limited due to a lack of understanding of the mechanical parameters that lead to cell membrane permeability.

Methods

We use a simple jet of inert gas to induce local transfection of plasmid DNA both in vitro (HeLa cells) and in vivo (chicken chorioallantoic membrane). Five different capillary tube inner diameters and three different gases were used to treat the cells to understand the dependency of transfection efficiency on the dynamic parameters.

Results

The simple setup has the advantage of allowing us to calculate the forces acting on cells during transfection. We found permeabilization efficiency was related to the dynamic pressure of the jet. The range of dynamic pressures that led to transfection in HeLa cells was small (200 ± 20 Pa) above which cell stripping occurred. We determined that the temporary pores allow the passage of dextran up to 40 kDa and reclose in less than 5 seconds after treatment. The optimized parameters were also successfully tested in vivo using the chorioallantoic membrane of the chick embryo.

Conclusions

The results show that the number of cells transfected with the plasmid scales with the dynamic pressure of the jet. Our results show that mechanical methods have a very small window in which cells are permeabilized without injury (200 to 290 Pa). This simple apparatus helps define the forces needed for physical cell transfection methods.

PLGA Nanoparticles for Ultrasound-Mediated Gene Delivery to Solid Tumors

This paper focuses on novel approaches in the field of nanotechnology-based carriers utilizing ultrasound stimuli as a means to spatially target gene delivery in vivo, using nanoparticles made with either poly(lactic-co-glycolic acid) (PLGA) or other polymers. We specifically discuss the potential for gene delivery by particles that are echogenic (amenable to destruction by ultrasound) composed either of polymers (PLGA, polystyrene) or other contrast agent materials (Optison, SonoVue microbubbles). The use of ultrasound is an efficient tool to further enhance gene delivery by PLGA or other echogenic particles in vivo. Echogenic PLGA nanoparticles are an attractive strategy for ultrasound-mediated gene delivery since this polymer is currently approved by the US Food and Drug Administration for drug delivery and diagnostics in cancer, cardiovascular disease, and also other applications such as vaccines and tissue engineering. This paper will review recent successes and the potential of applying PLGA nanoparticles for gene delivery, which include (a) echogenic PLGA used with ultrasound to enhance local gene delivery in tumors or muscle and (b) PLGA nanoparticles currently under development, which could benefit in the future from ultrasound-enhanced tumor targeted gene delivery.

Ultrasound-mediated delivery of echogenic immunoliposomes to porcine vascular smooth muscle cells in vivo

Vascular smooth muscle cells (VSMCs) are important targets in the treatment of atherosclerosis. However, the arterial media, where the majority of VSMCs reside, have proven to be a difficult target for drug/gene delivery. We have demonstrated that ultrasound enhances drug/gene delivery to VSMCs in vitro by using echogenic immunoliposomes (ELIPs) as the vector. This study aimed to evaluate whether ultrasound can similarly enhance the delivery of an agent to VSMCs, particularly within the arterial media, in vivo, using ELIP. Anti-smooth-muscle cell actin-conjugated calcein-loaded ELIP were injected into the peripheral arteries of Yucatan miniswine (n = 8 arterial pairs). The right-sided porcine arteries were treated with 1-MHz continuous-wave ultrasound at a peak-to-peak pressure amplitude of 0.23 +/- 0.05 MPa for 2 minutes. The contralateral arteries served as controls. Arteries were harvested after 30 minutes and imaged with fluorescence microscopy. Image data were converted to grayscale and analyzed by using computer-assisted videodensitometry. There was significant improvement in calcein uptake in all three arterial layers in the arteries exposed to ultrasound (> 300%). This enhanced uptake was site specific and appeared limited to the ultrasound-treated arterial segment. We have demonstrated enhanced delivery of a small molecule to VSMCs in all arterial wall layers, particularly the arterial media, using ultrasound and targeted ELIP. The combined effect of ultrasound exposure and ELIP as a contrast agent and a drug/gene-bearing vector has the potential for site-specific therapy directed at VSMC function.

Ultrasound microbubbles combined with liposome-mediated pNogo-R shRNA delivery into neural stem cells

In the present study, ultrasound-mediated microbubble destruction (UMMD) alone and combined with liposome technology was used as a novel nonviral technique to transfect a Nogo receptor (Nogo-R) shRNA plasmid (pNogo-R shRNA) into neural stem cells (NSCs). Using green fluorescent protein as a reporter gene, transfection efficiency of NSCs was significantly higher in the group transfected with UMMD combined with liposomes compared with that of the group transfected with UMMD or liposomes alone, and did not affect cell vitality. In addition, Nogo-R mRNA and protein expression was dramatically decreased in the UMMD combined with liposome-mediated group compared with that of other groups after 24 hours of transfection. The UMMD technique combined with liposomes is a noninvasive gene transfer method, which showed minimal effects on cell viability and effectively increased transfer of Nogo-R shRNA into NSCs.

Sonothrombolysis for the treatment of acute stroke: current concepts and future directions

Achieving rapid reperfusion transcranial color-coded duplex is the critical issue in acute stroke treatment. Ultrasound (US) generates negative pressure waves that are associated with an increase in either intrinsic or intravenous tissue plasminogen activator (tPA)-induced fibrinolytic activity. Higher rates of tPA-induced arterial recanalization, associated with a trend towards better functional outcome, have been safely achieved by using high-frequency US. By contrast, the use of low-frequency US and transcranial color-coded duplex has been linked to significant hemorrhagic complications. US-accelerated thrombolysis has been safely enhanced by lowering the amount of energy needed for acoustic cavitation with the administration of microbubbles. Other applications of US are being studied, including its intra-arterial use. Operator-independent devices, which will spread the use of these US techniques further, are also being developed. This article reviews the present status of sonothrombolysis in acute stroke treatment, highlighting both experimental and clinical studies addressing this issue, and discusses its future regarding both efficacy and safety.

Effect of microbubble contrast agent during high intensity focused ultrasound ablation on rabbit liver in vivo

OBJECTIVE

To evaluate the effect of a microbubble contrast agent (SonoVue) during HIFU ablation of a rabbit liver.

MATERIALS AND METHODS

HIFU ablations (intensity of 400W/cm(2) for 4s, six times, with a 5s interval between exposures) were performed upon 16 in vivo rabbit livers before and after intravenous injection of a microbubble contrast agent (0.8ml). A Wilcoxon signed rank test was used to compare mean ablation volume and time required to tissue ablation on real-time US. Shape of ablation and pattern of coagulative necrosis were analyzed by Fisher's exact test.

RESULTS

The volume of coagulative necrosis was significantly larger in the combination microbubble and HIFU group than in the HIFU alone group (P<0.05). Also, time to reach ablation was shorter in the combination microbubble and HIFU group than in the HIFU alone group (P<0.05). When analyzing the shape of tissue ablation, a pyramidal shape was more prevalently in the HIFU alone group compared to the combination microbubble and HIFU group (P<0.05). Following an analysis of the pattern of coagulative necrosis, non-cavitary necrosis was found in ten and cavitary necrosis in six of the samples in the combination microbubble and HIFU group. Conversely, non-cavitary necrosis occurred in all 16 samples in the HIFU alone group (P<0.05).

CONCLUSION

HIFU of in vivo rabbit livers with a microbubble contrast agent produced larger zones of ablation and more cavitary tissue necrosis than without the use of a microbubble contrast agent. Microbubble contrast agents may be useful in tissue ablation by enhancing the treatment effect of HIFU.

P85, Optison microbubbles and ultrasound cooperate in mediating plasmid DNA transfection in mouse skeletal muscles in vivo

Pluronic block copolymers, a kind of non-ionic surfactant, also known as poloxamers, and ultrasound-targeted microbubble destruction have been respectively investigated as vectors for gene delivery in vitro and in vivo. However, they are limited for clinical application due to the relatively low transfer efficiency of each individual vector. In the present study, we explored if the combination of P85, a pluronic block copolymer, Optison, a microbubble contrast agent and ultrasound enhances the transfection of plasmid DNA in vivo using mouse skeletal muscle models. Plasmid encoding green fluorescent protein (GFP) was respectively conjugated with 0.05%P85, 10%Optison, or 0.05%P85 plus 10%Optison, and injected into mouse tibialis anterior (TA) muscles with or without ultrasound irradiation (1 MHz, 1 W/cm(2), 2 min and 20% duty cycle). Mice were sacrificed 1 week after injection. The TA muscles were collected and cryo-sectioned into a series of 7 μm slices. To assess the efficiency of plasmid DNA transfection, tissue sections were counterstained with DAPI and scored by counting the number of GFP-positive fibers. Meanwhile the area of damaged muscles was measured based on the tissues stained with hematoxylin and eosin. Both P85 and Optison significantly enhanced the delivery of plasmid DNA in mouse TA skeletal muscles (P<0.01 and P<0.05 respectively, compared to saline control). In combination with Ultrasound irradiation, P85 (P<0.01, compared to P85 alone) but not Optison (P>0.05, compared to Optison alone) exerted a more pronounced effect on the transfection efficiency. Furthermore P85-induced gene delivery was higher than that by Optison regardless of the presence of ultrasound (P<0.01). The highest transfection efficiency was observed when P85, Optison and ultrasound irradiation were administrated together (P<0.01, compared to any other treatment in this study). The area of damaged muscles was enlarged by ultrasound irradiation in the presence of Optison microbubbles (P<0.01, compared to those groups without ultrasound irradiation). These results suggest that P85, microbubbles and ultrasound irradiation synergistically enhance plasmid DNA delivery in mouse skeletal muscles in vivo.

Characterizing bubble dynamics created by high-intensity focused ultrasound for the delivery of antibacterial nanoparticles into a dental hard tissue

Hig hintensity focused ultrasound (HIFU) has been applied for drug delivery in various disease conditions. Delivery of antibacterial-nanoparticles into dental hard tissues may open up new avenues in the treatment of dental infections. However, the basic mechanism of bubble dynamics, its characterization, and working parameters for effective delivery of nanoparticles, warrants further understanding. This study was conducted to highlight the basic concept of HIFU and the associated bubble dynamics for the delivery of nanoparticles. Characterization experiments to deliver micro-scale particles into simulated tubular channels, activity of ultrasonic bubbles, and pressure measurement inside the HIFU system were conducted. Subsequently, experiments were carried out to test the ability of HIFU to deliver nanoparticles into human dentine using field emission scanning electron micrographs (FESEM) and elemental dispersive X-ray analysis (EDX). The characterization experiments showed that the bubbles collapsing at the opening of tubular channels were able to propel particles along their whole length. The pressure measured showed sufficient negative and positive pressure suggesting that the bubble grew to a certain size before collapsing, thus enabling the particles to be pushed. The FESEM and EDX analysis highlighted the ability of HIFU to deliver nanoparticles deep within the dentinal tubules. This study highlighted the characteristics and the mechanism involved of the bubbles generated by the HIFU and their capability to deliver nanoparticles.

Optimum conditions of ultrasound-mediated destruction of bubble liposome for siRNA transfer in bladder cancer

Background: We investigated the effectiveness of ultrasound-mediated destruction of bubble liposome (UBL) for siRNA transfer by observing reduction in the luciferase activity of human bladder tumor RT-112 cells transfected with the luciferase gene (RT-112Luc) following luciferase siRNA transfer into the cells. Results: siRNA was transferred to 26% of RT-112Luc cells by UBL and the luciferase activity of RT-112Luc cells was significantly suppressed by UBL using the luciferase siRNA, compared with that using nonspecific siRNA in vitro (p = 0.036). The luciferase activity of RT-112Luc tumor was suppressed by UBL using luciferase siRNA compared with that using nonspecific siRNA 2 days after the in vivo treatment. Conclusion: This study showed that UBL is suitable for siRNA transfer to mammalian cells.

Delivery of stem cells to porcine arterial wall with echogenic liposomes conjugated to antibodies against CD34 and intercellular adhesion molecule-1

In atherosclerosis, the loss of vascular stem cells via apoptosis impairs the capacity of the vascular wall to repair or regenerate the tissue damaged by atherogenic factors. Recruitment of exogenous stem cells to the plaque tissue may repopulate vascular cells and help repair the arterial tissue. Ultrasound-enhanced liposomal targeting may provide a feasible method for stem cell delivery into atheroma. Bifunctional echogenic immunoliposomes (BF-ELIP) were generated by covalently coupling two antibodies to liposomes; the first one specific for CD34 antigens on the surface of stem cells and the second directed against the intercellular adhesion molecule-1 (ICAM-1) antigens on the inflammatory endothelium covering atheroma. CD34+ stem cells from adult bone marrow were incubated on the ICAM-1-expressing endothelium of the aorta of swine fed high cholesterol diets, which was preloaded with BF-ELIP. Significantly increased stem cell adherence and penetration were detected in particular in the aortic segments treated with 1 MHz low-amplitude continuous wave ultrasound. Fluorescence and scanning electron microscopy confirmed the presence of BF-ELIP-bound CD34+ cells in the intimal compartment of the atheromatous arterial wall. Ultrasound treatment increased the number of endothelial cell progenitors migrating into the intima. Thus, under ultrasound enhancement, BF-ELIP bound CD34+ stem cells selectively bind to the ICAM-1 expressing endothelium of atherosclerotic lesions.

Effects of ultrasound-induced inertial cavitation on enzymatic thrombolysis

Cavitation induced by ultrasound enhances enzymatic fibrinolysis by increasing the transport of reactants. However, the effects of cavitation need to be fully understood before sonothrombolysis can be applied clinically. In order to understand the underlying mechanisms, we examined the effects of combining ultrasound, microbubbles and thrombolytic enzymes on thrombolysis. First, we evaluated the relations between inertial cavitation and the reduction in the weight of a blood clot. Inertial cavitation was varied by changing the amplitude and duration of the transmitted acoustic wave as well as the concentration of microbubbles used to induce cavitation. Second, we studied the combined effects of streptokinase and inertial cavitation on thrombolysis. The results show that inertial cavitation increases the weight reduction of a blood clot by up to 33.9%. With linear regression fitting, the measured differential inertial cavitation dose and the weight reduction had a correlation coefficient of 0.66. Microscopically, enzymatic thrombolysis effects manifest as multiple large cavities within the clot that are uniformly distributed on the side exposed to ultrasound. This suggests that inertial cavitation plays an important role in producing cavities, while microjetting of the microbubbles induces pits on the clot surface. These observations preliminarily demonstrate the clinical potential of sonothrombolysis. The use of the differential inertial cavitation dose as an indicator of blood clot weight loss for controlled sonothrombolysis is also possible and will be further explored.

Transfection of cells in suspension by ultrasound cavitation

Sonoporation holds many promises in developing an efficient, reproducible and permanent gene delivery vector. In this study, we evaluated sonoporation as a method to transfect nucleic acids in suspension cells, including the human follicular lymphoma cell line RL and fresh human Chronic Lymphocytic Leukemia (CLL) cells. RL and CLL cells were exposed to continuous ultrasound waves (445 kHz) in the presence of either plasmid DNA coding for green fluorescent protein (GFP) or fluorescent siRNA directed against BCL2L1. Transfection efficiency and cell viability were assessed using fluorescent microscopy and flow cytometry analysis, respectively. Knock-down of target protein by siRNA was assessed by immunoblotting. Moreover, sonoporation was used to stably transfect RL cells with a plasmid coding for luciferase (pGL3). These cells were then used for the non-invasive monitoring of tumorigenesis in immunodeficient SCID mice. Sonoporation allows a highly efficient transfection of nucleic acid in suspension cells with a low rate of mortality, both in a tumor cell line and in fresh human leukemic cells. It also allowed efficient transfection of BCL2L1 siRNA with efficient reduction of the target protein level. In conclusion, ultrasound cavitation represents an efficient method for the transfection of cells in suspension, including fresh human leukemic cells.

Gene transfection to retinal ganglion cells mediated by ultrasound microbubbles in vitro

RATIONALE AND OBJECTIVES

To investigate the expression levels of green fluorescence protein (GFP) into retinal ganglion cells (RGCs) in vitro by ultrasound-mediated microbubble destruction (UMMD) and assess the effect of bcl-xl gene on N-methyl-D-aspartate (NMDA)-induced apoptosis in the cultured RGCs by UMMD.

MATERIALS AND METHODS

pEGFP-N1 was transfected to RGCs in vitro by UMMD and liposome was used as the control. The transfection effect was detected using microscope and flow cytometry qualitatively and quantitatively. Monotetrazolium was adopted to measure the cell vitality. NMDA was used to induce apoptosis in the cultured RGCs, and the bcl-xl gene was transfected into RGCs by UMMD before NMDA-induced apoptosis. The expression of bcl-xl protein in RGCs was assessed by immunohistochemistry assay. The amorphous character of RGCs was revealed by acridine orange and ethidium bromide staining. DNA fragment was detected by agarose gel electrophoresis.

RESULTS

Ultrasound combined with microbubbles enhanced gene transfection to the cultured cells in some condition. The average transfection rate of pEGFP-N1 with UMMD was 25%. Both ultrasound and microbubble had no effect on cell viability. The expression of bcl-xl protein in transfected and non-transfected RGCs was significantly different. Less apoptotic bodies and no representative DNA fragment were detected in the treatment group.

CONCLUSIONS

Microbubble destruction can enhance the reporter gene transfection and expression and have a good target. Transfection of bcl-xl gene has an anti-apoptosis effect on the cultured RGCs induced by NMDA with UMMD.

Application of ultrasonic gas-filled liposomes in enhancing transfer for breast cancer-related antisense oligonucleotides: an experimental study

The aim of this study was to investigate the application of ultrasonic gas-filled liposomes in enhancing transfer for breast cancer-related antisense oligonucleotides in vitro. An antisense oligodeoxynucleotide (AS-ODN) sequence, HA2741, modified with luciferase reporter plasmid, was used in evaluating the enhancing effect of gas-filled liposomes for gene transfer in breast cancer cells. Some important factors on HA 2741 transfection efficiency, such as wave intensity, ultrasound duration, gas-filled liposome concentration, and HA2741 concentration, were tested, respectively. Transfection efficiency was detected by fluorescence microscopy. Cell viability was verified by propidium iodide assay. Reverse-transcriptase polymerase chain reaction and immunocytochemistry were used to detect the inhibitory effect of HA2741 on HER-2 expression. All the four factors (wave intensity, ultrasound duration, gas-filled liposome concentration, and HA2741 concentration) showed a positive effect on AS-ODN transfection efficiency. However, these factors had a negative effect on cell viability. Considering all the factors investigated, the maximum transfection efficiency with minimum cell viability achieved under 2% gas-filled liposome mixed with 80 nmol/L HA2741 for 30-second ultrasound exposure at -3.0 dB wave intensity, which gave an overall transfection efficiency exceeding 90% and a cell viability near 90%. Under controlled conditions, ultrasound-mediated AS-ODN transfer, enhanced by gas-filled liposomes, may represent an effective, safe avenue for cancer-related gene delivery.

Examination of inertial cavitation of Optison in producing sonoporation of chinese hamster ovary cells

The objective of this project was to elucidate the relationship between ultrasound contrast agents (UCAs) and sonoporation. Sonoporation is an ultrasound-induced, transient cell membrane permeability change that allows for the uptake of normally impermeable macromolecules. Specifically, this study will determine the role that inertial cavitation plays in eliciting sonoporation. The inertial cavitation thresholds of the UCA, Optison, are compared directly with the results of sonoporation to determine the involvement of inertial cavitation in sonoporation. Chinese hamster ovary (CHO) cells were exposed as a monolayer in a solution of Optison, 500,000 Da fluorescein isothiocyanate-dextran (FITC-dextran), and phosphate-buffered saline (PBS) to 30 s of pulsed ultrasound at 3.15-MHz center frequency, 5-cycle pulse duration and 10-Hz pulse repetition frequency. The peak rarefactional pressure (P(r)) was varied over a range from 120 kPa-3.5 MPa, and five independent replicates were performed at each pressure. As the P(r) was increased, from 120 kPa-3.5 MPa, the fraction of sonoporated cells among the total viable population increased from 0.63-10.21%, with the maximum occurring at 2.4 MPa. The inertial cavitation threshold for Optison at these exposure conditions has previously been shown to be in the range 0.77-0.83 MPa, at which sonoporation activity was found to be 50% of its maximum level. Furthermore, significant sonoporation activity was observed at pressure levels below the threshold for inertial cavitation of Optison. Above 2.4 MPa, a significant drop in sonoporation activity occurred, corresponding to pressures where >95% of the Optison was collapsing. These results demonstrate that sonoporation is not directly a result of inertial cavitation of the UCA, rather that the effect is related to linear and/or nonlinear oscillation of the UCA occurring at pressure levels below the inertial cavitation threshold.

Micelles and nanoparticles for ultrasonic drug and gene delivery

Drug delivery research employing micelles and nanoparticles has expanded in recent years. Of particular interest is the use of these nanovehicles that deliver high concentrations of cytotoxic drugs to diseased tissues selectively, thus reducing the agent's side effects on the rest of the body. Ultrasound, traditionally used in diagnostic medicine, is finding a place in drug delivery in connection with these nanoparticles. In addition to their non-invasive nature and the fact that they can be focused on targeted tissues, acoustic waves have been credited with releasing pharmacological agents from nanocarriers, as well as rendering cell membranes more permeable. In this article, we summarize new technologies that combine the use of nanoparticles with acoustic power both in drug and gene delivery. Ultrasonic drug delivery from micelles usually employs polyether block copolymers and has been found effective in vivo for treating tumors. Ultrasound releases drug from micelles, most probably via shear stress and shock waves from the collapse of cavitation bubbles. Liquid emulsions and solid nanoparticles are used with ultrasound to deliver genes in vitro and in vivo. The small packaging allows nanoparticles to extravasate into tumor tissues. Ultrasonic drug and gene delivery from nanocarriers has tremendous potential because of the wide variety of drugs and genes that could be delivered to targeted tissues by fairly non-invasive means.

Ultrasonic gene and drug delivery to the cardiovascular system

Ultrasound targeted microbubble destruction has evolved as a promising tool for organ specific gene and drug delivery. This technique has initially been developed as a method in myocardial contrast echocardiography, destroying intramyocardial microbubbles to characterize refill kinetics. When loading similar microbubbles with a bioactive substance, ultrasonic destruction of microbubbles may release the transported substance in the targeted organ. Furthermore, high amplitude oscillations of microbubbles lead to increased capillary and cell membrane permeability, thus facilitating tissue and cell penetration of the released substance. While this technique has been successfully used in many organs, its application in the cardiovascular system has dominated so far. Drug delivery using microbubbles has played a minor role in the cardiovascular system. In contrast, gene transfer has been successfully achieved in many studies. Both viral and non-viral vectors were used for loading on microbubbles. This review article will give an overview on studies that have applied ultrasound targeted microbubble destruction to deliver substances in the heart and blood vessels. It will show potential therapeutic targets, especially for gene therapy, describe feasible substances that can be loaded on microbubbles, and critically discuss prospects and limitations of this technique.