Effects of dissolved gases and an echo contrast agent on ultrasound mediated in vitro gene transfection

A, Nayak UY. Low-Frequency Sonophoresis: A Promising Strategy for Enhanced Transdermal Delivery

Sonophoresis is the most approachable mode of transdermal drug delivery system, wherein low-frequency sonophoresis penetrates the drug molecules into the skin. It is an alternative method for an oral system of drug delivery and hypodermal injections. The cavitation effect is thought to be the main mechanism used in sonophoresis. The cavitation process involves forming a gaseous bubble and its rupture, induced in the coupled medium. Other mechanisms used are thermal effects, convectional effects, and mechanical effects. It mainly applies to transporting hydrophilic drugs, macromolecules, gene delivery, and vaccine delivery. It is also used in carrier-mediated delivery in the form of micelles, liposomes, and dendrimers. Some synergistic effects of sonophoresis, along with some permeation enhancers, such as chemical enhancers, iontophoresis, electroporation, and microneedles, increased the effectiveness of drug penetration. Sonophoresis-mediated ocular drug delivery, nail drug delivery, gene delivery to the brain, sports medicine, and sonothrombolysis are also widely used. In conclusion, while sonophoresis offers promising applications in diverse fields, further research is essential to comprehensively elucidate the biophysical mechanisms governing ultrasound-tissue interactions. Addressing these gaps in understanding will enable the refinement and optimization of sonophoresis-based therapeutic strategies for enhanced clinical efficacy.

Estimation of the number density of active cavitation bubbles in a sono-irradiated aqueous solution using a thermodynamic approach

An alternative semi-empirical technique is developed to determine the number density of active cavitation bubbles (N) formed in sonicated solutions. This was achieved by relating the acoustic power supplied to the solution (i.e., determined experimentally) to the released heat by a single bubble. The energy dissipation via heat exchange is obtained by an advanced cavitation model accounting for the liquid compressibility and viscosity, the non-equilibrium condensation/evaporation of water vapor, and heat conduction across the bubble wall and heats of chemical reactions resulting within the bubble at the collapse. A good concordance was observed between our results and those found in the literature. It was found that the number of active bubbles increased proportionally with a rise in ultrasound frequency. Additionally, the increase of acoustic intensity increases the number of active bubbles, whatever the sonicated solution's volume. On the other hand, it was observed that the rise of the irradiated solution volume causes the number of active bubbles to be reduced even when the acoustic power is increased. A decrease in acoustic energy accelerates this negative impact.

Numerical simulation of single bubble dynamics under acoustic travelling waves

The objective of this paper is to apply CLSVOF method to investigate the single bubble dynamics in acoustic travelling waves. The Naiver-Stokes equation considering the acoustic radiation force is proposed and validated to capture the bubble behaviors. And the CLSVOF method, which can capture the continuous geometric properties and satisfies mass conservation, is applied in present work. Firstly, the regime map, depending on the dimensionless acoustic pressure amplitude and acoustic wave number, is constructed to present different bubble behaviors. Then, the time evolution of the bubble oscillation is investigated and analyzed. Finally, the effect of the direction and the damping coefficient of acoustic wave propagation on the bubble behavior are also considered. The numerical results show that the bubble presents distinct oscillation types in acoustic travelling waves, namely, volume oscillation, shape oscillation, and splitting oscillation. For the splitting oscillation, the formation of jet, splitting of bubble, and the rebound of sub-bubbles may lead to substantial increase in pressure fluctuations on the boundary. For the shape oscillation, the nodes and antinodes of the acoustic pressure wave contribute to the formation of the "cross shape" of the bubble. It should be noted that the direction of the bubble translation and bubble jet are always towards the direction of wave propagation. In addition, the damping coefficient causes bubble in shape oscillation to be of asymmetry in shape and inequality in size, and delays the splitting process.

Biologically and Acoustically Compatible Chamber for Studying Ultrasound-Mediated Delivery of Therapeutic Compounds

Ultrasound (US), in combination with microbubbles, has been found to be a potential alternative to viral therapies for transfecting biological cells. The translation of this technique to the clinical environment, however, requires robust and systematic optimization of the acoustic parameters needed to achieve a desired therapeutic effect. Currently, a variety of different devices have been developed to transfect cells in vitro, resulting in a lack of standardized experimental conditions and difficulty in comparing results from different laboratories. To overcome this limitation, we propose an easy-to-fabricate and cost-effective device for application in US-mediated delivery of therapeutic compounds. It comprises a commercially available cell culture dish coupled with a silicon-based "lid" developed in-house that enables the device to be immersed in a water bath for US exposure. Described here are the design of the device, characterization of the sound field and fluid dynamics inside the chamber and an example protocol for a therapeutic delivery experiment.

Effect of sonication conditions: solvent, time, temperature and reactor type on the preparation of micron sized vermiculite particles

The effects of temperature, time, solvent and sonication conditions under air and Argon are described for the preparation of micron and sub-micron sized vermiculite particles in a double-jacketed Rosett-type or cylindrical reactor. The resulting materials were characterized via X-ray powder diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared (FTIR) Spectroscopy, BET surface area analysis, chemical analysis (elemental analysis), Thermogravimetry analysis (TGA) and Laser Granulometry. The sonicated vermiculites displayed modified particle morphologies and reduced sizes (observed by scanning electron microscopy and laser granulometry). Under the conditions used in this work, sub-micron sized particles were obtained after 5h of sonication, whereas longer times promoted aggregation again. Laser granulometry data revealed also that the smallest particles were obtained at high temperature while it is generally accepted that the mechanical effects of ultrasound are optimum at low temperatures according to physical/chemical properties of the used solvent. X-ray diffraction results indicated a reduction of the crystallite size along the basal direction [001]; but structural changes were not observed. Sonication at different conditions also led to surface modifications of the vermiculite particles brought out by BET surface measurements and Infrared Spectroscopy. The results indicated clearly that the efficiency of ultrasound irradiation was significantly affected by different parameters such as temperature, solvent, type of gas and reactor type.

Dissolved gas and ultrasonic cavitation--a review

The physics and chemistry of nonlinearly oscillating acoustic cavitation bubbles are strongly influenced by the dissolved gas in the surrounding liquid. Changing the gas alters among others the luminescence spectrum, and the radical production of the collapsing bubbles. An overview of experiments with various gas types and concentration described in literature is given and is compared to mechanisms that lead to the observed changes in luminescence spectra and radical production. The dissolved gas type changes the bubble adiabatic ratio, thermal conductivity, and the liquid surface tension, and consequently the hot spot temperature. The gas can also participate in chemical reactions, which can enhance radical production or luminescence of a cavitation bubble. With this knowledge, the gas content in cavitation can be tailored to obtain the desired output.

Targeted microbubbles in the experimental and clinical setting

BACKGROUND

Microbubbles have improved ultrasonography imaging techniques over the past 2 decades. Their safety, versatility, and easiness of use have rendered them equal or even superior in some instances to other imaging modalities such as computed tomography and magnetic resonance imaging. Herein, we conducted a literature review to present their types, general behavior in tissues, and current and potential use in clinical practice.

METHODS

A literature search was conducted for all preclinical and clinical studies involving microbubbles and ultrasonography.

RESULTS

Different types of microbubbles are available. These generally improve the enhancement of tissues during ultrasonography imaging. They also can be attached to ligands for the target of several conditions such as inflammation, angiogenesis, thrombosis, apoptosis, and might have the potential of carrying toxic drugs to diseased sites, thereby limiting the systemic adverse effects.

CONCLUSIONS

The use of microbubbles is evolving rapidly and can have a significant impact on the management of various conditions. The potential for their use as targeting agents and gene and drug delivery vehicles looks promising.

Sonoporation, drug delivery, and gene therapy

Ultrasound is a very effective modality for drug delivery and gene therapy because energy that is non-invasively transmitted through the skin can be focused deeply into the human body in a specific location and employed to release drugs at that site. Ultrasound cavitation, enhanced by injected microbubbles, perturbs cell membrane structures to cause sonoporation and increases the permeability to bioactive materials. Cavitation events also increase the rate of drug transport in general by augmenting the slow diffusion process with convective transport processes. Drugs and genes can be incorporated into microbubbles, which in turn can target a specific disease site using ligands such as the antibody. Drugs can be released ultrasonically from microbubbles that are sufficiently robust to circulate in the blood and retain their cargo of drugs until they enter an insonated volume of tissue. Local drug delivery ensures sufficient drug concentration at the diseased region while limiting toxicity for healthy tissues. Ultrasound-mediated gene delivery has been applied to heart, blood vessel, lung, kidney, muscle, brain, and tumour with enhanced gene transfection efficiency, which depends on the ultrasonic parameters such as acoustic pressure, pulse length, duty cycle, repetition rate, and exposure duration, as well as microbubble properties such as size, gas species, shell material, interfacial tension, and surface rigidity. Microbubble-augmented sonothrombolysis can be enhanced further by using targeting microbubbles.

New development of 'sono-functional' molecule: binding to DNA by sonication

'Sono-functional' molecule 1 was prepared and its binding properties to DNA under ultrasonic irradiation were studied by UV spectra. As a result, it was shown that the binding of 1 to DNA was enhanced by ultrasound. Being compared with its precursor 2, it is clear that terminal thiol groups of 1 play an important role in specific binding to DNA.

Ultrasound-mediated gene transfection

Ultrasound-mediated gene transfection (sonotransfection) has been shown to be a promising physical method for gene therapy, especially for cancer gene therapy. The procedure being done in vitro uses several ultrasound exposure (sonication) setups. Although high transfection rates have been attained in some of these setups in vitro, replicating similar levels of transfection in vivo has been difficult. In vivo-simulated setups offer hope for a more consistent outcome in vivo. Presented in this chapter are typical methods of sonotransfection in vitro, methods when using a novel in vivo-simulated in vitro sonication setup and also sonotransfection methods when doing in vivo experiments. Factors that could potentially influence the outcome of an ultrasound experiment are cited. Several advantages of sonotransfection are recognized, although a low transfection rate is still considered a disadvantage of this method. To improve the transfection rate and the efficiency of sonotransfection, several studies are currently being undertaken. Particularly promising are studies using engineered microbubbles to carry the therapeutic genes into a particular target tissue in the body, then using ultrasound to release or deliver the genes directly into target cells, e.g., cancer cells.

Ultrasound attenuation estimation using backscattered echoes from multiple sources

The objective of this study was to devise an algorithm that can accurately estimate the attenuation along the propagation path (i.e., the total attenuation) from backscattered echoes. It was shown that the downshift in the center frequency of the backscattered ultrasound echoes compared to echoes obtained in a water bath was calculated to have the form Deltaf=mf(o)+b after normalizing with respect to the source bandwidth where m depends on the correlation length, b depends on the total attenuation, and f(o) is the center frequency of the source as measured from a reference echo. Therefore, the total attenuation can be determined independent of the scatterer correlation length by measuring the downshift in center frequency from multiple sources (i.e., different f(o)) and fitting a line to the measured shifts versus f(o). The intercept of the line gives the total attenuation along the propagation path. The calculations were verified using computer simulations of five spherically focused sources with 50% bandwidths and center frequencies of 6, 8, 10, 12, and 14 MHz. The simulated tissue had Gaussian scattering structures with effective radii of 25 mum placed at a density of 250 mm(3). The attenuation of the tissue was varied from 0.1 to 0.9 dB / cm-MHz. The error in the attenuation along the propagation path ranged from -3.5+/-14.7% for a tissue attenuation of 0.1 dB / cm-MHz to -7.0+/-3.1% for a tissue attenuation of 0.9 dB / cm-MHz demonstrating that the attenuation along the propagation path could be accurately determined using backscattered echoes from multiple sources using the derived algorithm.

Effects of ultrasound on apoptosis induced by anti-CD20 antibody in CD20-positive B lymphoma cells

AIM

The present study was conducted to examine the thermal and non-thermal effects of ultrasound on apoptosis induced by anti-CD20 monoclonal antibody (rituximab).

MATERIALS AND METHODS

SU-DHL-4 cells, a CD20-positive cell line derived from B cell lymphomas with a BCL2 gene rearrangement, were exposed to continuous 1 MHz ultrasound for therapeutic use under an air- or CO(2)-saturated condition to control cavitation. Early apoptosis (EA) and secondary necrosis (SN) were examined by flow cytometry. Cavitation was determined by detecting the hydroxyl radicals derived from pyrolysis of water molecules using electron paramagnetic resonance-spin trapping. To assess thermal effects, cells were treated in a temperature-controlled water bath.

RESULTS

There was a significant additive increase in EA and EA+SN observed in cells treated with rituximab combined with heat at 42 degrees C or non-thermal ultrasound at 0.5 W/cm(2) under an air-saturated condition, where heat or ultrasound induced some cell death. A significant synergistic increase in EA and EA+SN was observed in cells treated with rituximab and ultrasound at 2.5 W/cm(2) under CO(2)-saturated conditions, where inertial cavitations were completely suppressed. No enhancement was observed at a temperature less than 40 degrees C or ultrasound at 0.5 W/cm(2) under CO(2)-saturated conditions.

CONCLUSION

These results suggest that the immuno-therapeutic application of ultrasound at relatively high-intensities combined with rituximab thus produces synergistic effects under conditions where the non-thermal and non-cavitational effects are predominant.

Transfection effect of microbubbles on cells in superposed ultrasound waves and behavior of cavitation bubble

The combination of ultrasound and ultrasound contrast agents (UCAs) is able to induce transient membrane permeability leading to direct delivery of exogenous molecules into cells. Cavitation bubbles are believed to be involved in the membrane permeability; however, the detailed mechanism is still unknown. In the present study, the effects of ultrasound and the UCAs, Optison on transfection in vitro for different medium heights and the related dynamic behaviors of cavitation bubbles were investigated. Cultured CHO-E cells mixed with reporter genes (luciferase or beta-gal plasmid DNA) and UCAs were exposed to 1 MHz ultrasound in 24-well plates. Ultrasound was applied from the bottom of the well and reflected at the free surface of the medium, resulting in the superposition of ultrasound waves within the well. Cells cultured on the bottom of 24-well plates were located near the first node (displacement node) of the incident ultrasound downstream. Transfection activity was a function determined with the height of the medium (wave traveling distance), as well as the concentration of UCAs and the exposure time was also determined with the concentration of UCAs and the exposure duration. Survival fraction was determined by MTT assay, also changes with these values in the reverse pattern compared with luciferase activity. With shallow medium height, high transfection efficacy and high survival fraction were obtained at a low concentration of UCAs. In addition, capillary waves and subsequent atomized particles became significant as the medium height decreased. These phenomena suggested cavitation bubbles were being generated in the medium. To determine the effect of UCAs on bubble generation, we repeated the experiments using crushed heat-treated Optison solution instead of the standard microbubble preparation. The transfection ratio and survival fraction showed no additional benefit when ultrasound was used. These results suggested that cavitation bubbles created by the collapse of UCAs were a key factor for transfection, and their intensities were enhanced by the interaction of the superpose ultrasound with the decreasing the height of the medium. Hypothesizing that free cavitation bubbles were generated from cavitation nuclei created by fragmented UCA shells, we carried out numerical analysis of a free spherical bubble motion in the field of ultrasound. Analyzing the interaction of the shock wave generated by a cavitation bubble and a cell membrane, we estimated the shock wave propagation distance that would induce cell membrane damage from the center of the cavitation bubble.

Transient permeabilization of cell membranes by ultrasound-exposed microbubbles is related to formation of hydrogen peroxide

In the present study, we addressed the interactions among ultrasound, microbubbles, and living cells as well as consequent arising bioeffects. We specifically investigated whether hydrogen peroxide (H(2)O(2)) is involved in transient permeabilization of cell membranes in vitro after ultrasound exposure at low diagnostic power, in the presence of stable oscillating microbubbles, by measuring the generation of H(2)O(2) and Ca(2+) influx. Ultrasound, in the absence or presence of SonoVue microbubbles, was applied to H9c2 cells at 1.8 MHz with a mechanical index (MI) of 0.1 or 0.5 during 10 s. This was repeated every minute, for a total of five times. The production of H(2)O(2) was measured intracellularly with CM-H(2)DCFDA. Cell membrane permeability was assessed by measuring real-time changes in intracellular Ca(2+) concentration with fluo-4 using live-cell fluorescence microscopy. Ultrasound, in the presence of microbubbles, caused a significant increase in intracellular H(2)O(2) at MI 0.1 of 50% and MI 0.5 of 110% compared with control (P < 0.001). Furthermore, we found increases in intracellular Ca(2+) levels at both MI 0.1 and MI 0.5 in the presence of microbubbles, which was not detected in the absence of extracellular Ca(2+). In addition, in the presence of catalase, Ca(2+) influx immediately following ultrasound exposure was completely blocked at MI 0.1 (P < 0.01) and reduced by 50% at MI 0.5 (P < 0.001). Finally, cell viability was not significantly affected, not even 24 h later. These results implicate a role for H(2)O(2) in transient permeabilization of cell membranes induced by ultrasound-exposed microbubbles.

Ultrasound enhances liposome-mediated gene transfection

Previous studies have shown that some series of liposomes, usually containing cationic lipids, are useful tools for gene introduction into cells. To investigate the effect of ultrasound (US) on liposome-mediated transfection, three types of liposomes (designated L1, L2 and L3, in the order of increasing transfection efficiency) containing O,O'-ditetradecanoyl-N-(alpha-trimethylammonioacetyl) diethanolamine chloride, dioleoylphosphatidylethanolamine, and/or cholesterol at varying ratios, were used in this study. HeLa cells were treated with liposome-DNA complexes containing luciferase genes for 2 h before sonication. Optimal US condition for the enhancement was determined to be 0.5 W/cm2, 1 MHz continuous wave for 1 min and was above threshold for inertial cavitation based on EPR detection of free radicals. Luciferase expressions 24 h after the treatments were significantly increased by sonication to 2.4 fold with L1, and 1.7 fold with L2. However, with L3, which showed the highest level of expression among the liposomes, significant but minimal enhancement was observed when sonication was done 15 min after the DNA-L3 treatment, suggesting that efficiency of the liposome also determines the proper timing for sonication. The 2 h pre-sonication incubation with liposome-DNA complexes for L1 and L2 (30 min for L3) required to attain enhancement, suggests that US works to enhance transfection only after cells had enough DNA uptake.

Biological effects of low intensity ultrasound: the mechanism involved, and its implications on therapy and on biosafety of ultrasound

The biological effects of low intensity ultrasound (US) in vitro; the mechanisms involved; and the factors that can enhance or inhibit these effects are reviewed. The lowest possible US intensities required to induce cell killing or to produce free radicals were determined. Following sonication in the region of these intensities, the effects of US in combination with either hyperthermia, hypotonia, echo-contrast agents (ECA), CO2, incubation time, high cell density or various agents were examined. The results showed that hyperthermia, hypotonia and microbubbles are good enhancers of the bioeffects, while CO2, incubation time and high cell density are good inhibitors. Cellular membrane damage is pivotal in the events leading to cell death, with the cellular damage-and-repair mechanism as an important determinant of the fate of the damaged cells. The optimal level of apoptosis (with minimal lysis) and optimal gene transfection efficiency were attained using a pulsed low intensity US. In summary, the findings suggest that low intensity US is potentially useful in therapy, while on the other hand, they also call for further investigation of such clinical scenarios as high-grade fever, edema or use of ECA which may lead to the lowering of the threshold for bioeffects with diagnostic US.

A novel approach to quantitative ultrasonic naked gene delivery and its non-invasive assessment

The purpose of this study was to investigate practical, safe, easy-to-use, non-cytotoxic, and reliable parameters to apply to an ultrasound (US) naked gene therapy system. The ultrasound pressure at the point of cell exposure was measured using a calibrated hydrophone and the intensity calculated. An acoustic power meter calibrated using a hydrophone was used to measure the power of the transducer. Four cell types were exposed to US with different exposure times and intensities. Fluorescent microscopy, spectrophotometry, scanning electron microscope, laser scanning confocal microscopy, flow cytometry and histogram analysis were used to evaluate the results of the study. The plasmid of green fluorescent protein (GFP) served as the reporter gene. The energy accumulation E in US gene delivery for 90% cell survival was defined as the optimal parameters (E=3.56+/-0.06), and at 80% cell survival was defined as the damage threshold (E=59.67+/-3.54). US safely delivered GFP into S180 cells (35.1 kHz) at these optimal parameters without obvious damage or cytotoxity in vitro. Exposed cell function was proved normal in vivo. The transfection rate was 35.83+/-2.53% (n=6) in viable cells, corresponding to 90.17+/-1.47% (n=6) cell viability. The intensity of GFP expression showed a higher fluorescent peak in the group of adeno-associated virus GFP vector (AVV-GFP) than in the control group (P<0.001). The effect of US gene delivery and cell viability correlated as a fifth order polynomial with US intensity and exposure time. With optimal parameters, US can safely deliver naked a gene into a cell without damage to cell function. Both optimal uptake and expression of gene depend on the energy E at 90% cell survival. E can be applied as a control factor for bioeffects when combined with other parameters. Stable caviation results in optimal parameters for gene delivery and the transient caviation may cause cell damage, which will bring about a sharp rise of permeabilization. The results may be applied to the development of a novel clinical gene therapeutic system.

Ultrasound mediated intravesical transfection enhanced by treatment with lidocaine or heat

PURPOSE

We have previously reported that cell membrane modification by lidocaine or heat can enhance ultrasound mediated transfection (USMT) on PC-3 cells in vitro. In the current study we investigated whether such enhancement could be observed using the T24 human bladder cancer cell line in vitro along with PC-3 in vivo.

MATERIALS AND METHODS

For in vitro transfection T24 cells were sonicated with 1 MHz ultrasound at 3.6 W/cm (ISATA) for 20 seconds. For in vivo transfection T24 or PC-3 cells in the bladder were transabdominally sonicated with 1 MHz ultrasound at 0.78 W/cm (ISATA) for 60 seconds. Transfection efficiency was evaluated by the luciferase assay standardized with protein contents of the samples.

RESULTS

Lidocaine or heat treatment of T24 cells during sonication enhanced luciferase expression significantly. Results indicated that enhancements could be achieved in a different cell line, although to lesser degrees than with PC-3 cells. In addition, membrane fluidity facilitation and cell viability after sonication were also different, presumably influenced by the different structures and/or compositions of the cell membranes. PC-3 and T24 cells were successfully transfected in the bladder. In addition, USMT enhancements were also observed in the 2 cell lines when sonicated with lidocaine or heat.

CONCLUSIONS

These results suggest that USMT and its enhancement with lidocaine or heat can be applied for gene therapy in the bladder.

Emerging technologies in therapeutic ultrasound: thermal ablation to gene delivery

Ultrasound is used today in medicine as a modality for diagnostic imaging. Recently, there have been numerous reports on the application of thermal and nonthermal ultrasound energy for treating various diseases. In addition to thermal ablation of tumors, non-thermal ultrasound combined with drugs and genes have led to much excitement especially for cancer treatment, vascular diseases, and regenerative medicine. Ultrasound energy can enhance the effects of thrombolytic agents such as urokinase for treatment of stroke and acute myocardial infarction. New ultrasound technologies have resulted in advanced devices such as a) ultrasound catheters, b) Non-invasive methods as high intensity focused ultrasound (HIFU) in conjunction with MRI and CT is already being applied in the clinical field, c) Chemical activation of drugs by ultrasound energy for treatment of tumors is another new field recently termed "Sonodynamic Therapy", and d) Combination of genes and microbubble have induced great hopes for ideal gene therapy (sonoporation). Various examples of ultrasound combined modalities are under investigation which could lead to revolutionary therapy.

Interrelation between HeLa-S3 cell transfection and hemolysis in red blood cell suspension using pulsed ultrasound of various duty cycles

We have studied the in vitro transfection of a plasmid DNA with the lacZ gene to HeLa-S3 cells and hemolysis in a red blood cell (RBC) suspension under pulsed ultrasound with duty cycles gamma of 10, 20 and 30% using a digital sonifier at a frequency of 20 kHz and an intensity of 6.2 W/cm(2) on the surface of a horn tip. Cultured HeLa-S3 cells in suspension were exposed to pulsed ultrasound for an apparent exposure time t' from 0 to 60 s. HeLa-S3 viability decreased as a single exponential function of the total exposure time t = gammat' with a common time constant tau = 3.8 s for three duty cycles. Transfection was evaluated by counting the number of beta-galactosidase(beta-Gal)-positive cells relative to the total number of cells. Pulsed ultrasound provided an enhanced transfer of the beta-Gal plasmid to HeLa-S3 cells, 3.4-fold as compared with that in the case of the control. The optimal transfection efficiencies were 0.75, 0.80 and 0.74% near t = tau with gamma = 10, 20 and 30%, respectively. The number ratio of beta-Gal-positive cells to the surviving cells after exposure increased with t' according to a modified logistic equation. The degree of hemolysis also increased exponentially with t' at a time constant tau' = tau(0)/gamma for the RBC suspension in physiological saline at a hematocrit concentration of 0.5% with tau(0) = 0.9 s. Thus the total exposure time for the optimal transfection efficiency was tau, that is, nearly four times of tau(0). Hemolysis in the RBC suspension may be a useful model for determining optimal transfection by pulsed ultrasound of various duty cycles.

Enhancement of ultrasound-mediated gene transfection by membrane modification

BACKGROUND

Ultrasound-mediated gene transfection (USMGT) with an echo contrast agent could be a new promising physical method of triggering localized gene delivery, but the effect is still modest. The aim of this study is to devise a method to improve efficiency of USMGT. We examined the effect of lidocaine and different temperatures on USMGT, each of which is a known membrane modifier, since the plasma membrane can be considered a site of action in USMGT.

METHODS

We observed the effect of lidocaine (0.01, 0.1 or 1.0 mM) and different temperatures (7, 20, 37, 42 or 44 degrees C) on USMGT (1 MHz, 3.6 W/cm(2) (I(SATA)) and 20 s exposure) in the presence of Levovist (10 mg/ml). At 20 h after sonication, transfection efficiency was evaluated by luciferase assay. Membrane fluidity was examined by fluorescence polarization measurement. Cavitational activity was measured by ESR spin trapping with 5,5-dimethyl-1-pyrroline N-oxide. The number of cells transfected with the GFP gene was counted under a fluorescence microscope.

RESULTS

Lidocaine (1 mM) and heat (42-44 degrees C) significantly increased luciferase expression approximately 18-fold and 19-fold higher than Levovist only. Both treatments were shown to increase membrane fluidity; in addition, heat enhanced a cavitational effect. It was confirmed by an experiment using the GFP gene that increase in luciferase expression was due to the increase in number of cells.

CONCLUSIONS

This enhancement could be useful for ultrasound-mediated gene therapy in the future since both treatments for membrane modification could be directly applied to the living body.

Enhanced ultrasound-induced apoptosis and cell lysis by a hypotonic medium

PURPOSE

To test the hypothesis that non-lethal hypotonia will enhance ultrasound-induced cell killing in vitro and that the mechanism is mechanical in nature.

MATERIALS AND METHODS

Hypotonic RPMI medium (146 mOsm) was used to induce non-lethal osmotic swelling of human myelomonocytic leukaemia U937 cells. Hypotonia for 10 min was started just before exposure to 1 MHz ultrasound at 0.5 or 1.0 Wcm(-2) for 10 min, or 5 min before exposure to 2.0 Wcm(-2) for 1 min. Surviving intact cells were then determined by the trypan blue dye exclusion test immediately after treatment. After 6-h incubation of the treated cells, early apoptosis and secondary necrosis were measured using a flow cytometer. Intracellular free calcium ion imaging by Fura-2 fluorescence and cellular ion scanning using a secondary ion mass spectrometer were also performed.

RESULTS

Enhancement of ultrasound-induced cell lysis was observed at all intensities, and most prominently at 2.0 Wcm(-2), while apoptosis induction was significantly enhanced at intensities of 0.5 and 1.0 Wcm(-2), but not at 2.0 Wcm(-2). The enhanced cell lysis is attributed to the increased susceptibility of the cells to mechanical damage. This is consistent with previous reports describing the effects of mechanical stresses on cell membranes. Cellular ion scanning images also suggest that hypotonia has an effect on the membrane damage-and-repair mechanism of the cells.

CONCLUSIONS

The results support the hypothesis that non-lethal hypotonia can enhance ultrasound-induced cell killing. These findings also suggest the 'sonomechanical' nature of the effects on the cells.

Ultrasound-induced killing of monocytic U937 cells enhanced by 2,2'-azobis(2-amidinopropane) dihydrochloride

To determine the effect of 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) on ultrasound (US)-induced cell killing, human monocytic leukemia cells (U937) were incubated at various temperatures (25.0, 37.0 and 40.0 degrees C) for 1 min in air-saturated phosphate-buffered solution (PBS) containing 50 mM AAPH before exposure to nonthermal 1 MHz US for 1 min at an intensity of 2.0 W/cm(2). Cell viability was determined by means of the Trypan blue dye exclusion test immediately after sonication. Apoptosis was measured after 6-h incubation post-sonication by flow cytometry. Free radicals generated by AAPH, a temperature-dependent free radical generator, or US or both were also investigated using electron paramagnetic resonance (EPR) spin trapping. The results showed that US-induced cell lysis and apoptosis were enhanced in the presence of AAPH regardless of the temperature at the time of sonication. At 40.0 degrees C, US alone induced increased cell killing, while AAPH alone is capable of inducing significant but minimal apoptosis at this temperature. Although free radicals were increased in the combined treatment, this increase did not correlate well with cell killing. The mechanism of enhancement points to the increased uptake of the agent during sonication rather than potentiation by AAPH. These findings suggest the clinical potential of temperature-dependent free radical generators in cancer therapy with therapeutic US.

Ultrasound-enhanced transgene expression in vascular cells is not dependent upon cavitation-induced free radicals

Although acoustic cavitation is clearly important in ultrasound (US)-enhanced gene delivery (UEGD), the relative importance of mechanical and sonochemical (free radical) bioeffects remains unclear, as does the mechanism of gene delivery at the cellular level. Porcine vascular smooth muscle cells (VSMC) were transfected with luciferase or green fluorescent protein (GFP) plasmid +/- pulsed 956 kHz US (2.0 mechanical index (MI), 128 W cm(-2) spatial peak pulse average intensity, ISPPA) for 60 s, in the presence or absence of 20 mM cysteamine or N-acetyl-L-cysteine. Both compounds effectively scavenged free radical production following US, leaving unaffected the 50- to 100-fold enhancements in luciferase expression seen in US-treated VSMC. US exposure enhanced plasmid uptake (25 +/- 4.6 vs. 3 +/- 1.9 cells/field, n=4, p<0.05), most likely directly into the cytoplasm, and increased both the total number (>sevenfold) and average fluorescence intensity (>sixfold) of GFP-transfected cells. UEGD is not dependent upon cavitation-induced free radical generation and has potential for use with a wide range of therapeutic transgenes.

Focused ultrasound (HIFU) induces localized enhancement of reporter gene expression in rabbit carotid artery

The development of accurate, safe, and efficient gene delivery remains a major challenge towards the realization of gene therapeutic prevention and treatment of cardiovascular diseases. In this study, we investigated the ability of high-intensity focused ultrasound (HIFU), a form of mechanical wave transmission, to act as a noninvasive tool for the enhancement of in vivo gene transfer into rabbit carotid arteries. Segments of the common carotid arteries of New Zealand white rabbits were isolated and infused with plasmid DNA encoding the reporter beta-galactosidase either with or without the addition of ultrasound contrast agent consisting of small (approximately 2-5 microm) gas-filled human albumin microspheres to augment cavitation. Infused arteries were exposed to pulsed ultrasound for 1 min (frequency 0.85 MHz, burst length 50 ms, repetition frequency 1 Hz, duration 60 s, peak pressure amplitude of 15 MPa). At 6.3 MPa, HIFU enhanced gene expression eight-fold, and 17.5-fold in the presence of contrast. We found increasing amounts of beta-galactosidase expression in the carotid vessel with increasing pressure amplitude. This dose-response relation was present with and without contrast. Without contrast, no vessel damage was detected up to 15 MPa, while the addition of contrast induced side effects above a threshold of 6.3 MPa peak pressure. The entire procedure was feasible and safe for the animals, and the results suggest that HIFU has the potential to assist in the noninvasive spatial regulation of gene transfer into the vascular system.