Ultrasound, microbubbles and the blood-brain barrier

The blood–brain barrier (BBB) is a specialized system of capillary endothelial cells that protects the brain from harmful substances in the blood stream, while supplying the brain with the required nutrients for proper function. The BBB controls transport through both tight junctions and metabolic barriers and is often a rate-limiting factor in determining permeation of therapeutic drugs into the brain. It is a significant obstacle for delivery of both small molecules and macromolecular agents. Although many drugs could be potentially used to treat brain disease, there has been no method that allows non-invasive-targeted delivery through the BBB. Recently, promising studies indicate that ultrasound can be used to locally deliver a drug or gene to a specific region of interest in the brain. If microbubbles are combined with ultrasound exposure, the effects of ultrasound can be focused upon the vasculature to reduce the acoustic intensity needed to produce BBB opening. Several avenues of transcapillary passage after ultrasound sonication have been identified including transcytosis, passage through endothelial cell cytoplasmic openings, opening of tight junctions and free passage through injured endothelium. This article reviews the topic of transient disruption of the BBB with ultrasound and microbubbles and addresses related safety issues. It also discusses possible roles of the BBB in brain disease and potential interactions with ultrasound and microbubbles in such disease states.     

Ultrasound and matter--physical interactions

The basic physical characteristics of ultrasound waves are reviewed in terms of the typical displacements, velocities, accelerations and pressures generated in various fluid media as a function of frequency. The effects on wave propagation of interfaces are considered, and the way in which waves are reflected, transmitted and mode converted at interfaces introduced. Then the nonlinear propagation of high amplitude ultrasound is explained, and its consequences, including the generation of harmonic frequencies and enhanced attenuation, considered. The absorption of ultrasonic waves and the resulting heat deposition in absorbing media are described together with factors determining the resulting temperature rises obtained. In the case of tissue these include conduction and perfusion. The characteristics of cavitation in fluid media are also briefly covered. Finally, secondary nonlinear physical effects are described. These include radiation forces on interfaces and streaming in fluids.     

Ultrasound-mediated interferon β gene transfection inhibits growth of malignant melanoma

We investigated the effects of ultrasound-mediated transfection (sonotransfection) of interferon β (IFN-β) gene on melanoma (C32) both in vitro and in vivo. C32 cells were sonotransfected with IFN-β in vitro. Subcutaneous C32 tumors in mice were sonicated weekly immediately after intra-tumor injection with IFN-β genes mixed with microbubbles. Successful sonotransfection with IFN-β gene in vitro was confirmed by ELISA, which resulted in C32 growth inhibition. In vivo, the growth ratio of tumors transfected with IFN-β gene was significantly lower than the other experimental groups. These results may lead to a new method of treatment against melanoma and other hard-to-treat cancers.     

Solvent-controlled regioselective protection of 5'-O-protected thymidine

This paper describes an efficient procedure for selective 3'-O- or 3-N-protection of 5'-O-tert-butyldimethylsilylthymidine, depending on the use of aprotic polar solvents with low or high dielectric constant, respectively. These syntheses were activated by either ultrasound or microwaves. Several alkyl bromides offer a convenient route to prepare 3'-O- or 3-N-protected and functionalized thymidine derivatives.     

Ultrasound enhanced methanol penetration of zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>) embryos measured by permittivity changes using impedance spectroscopy

Studies on permittivity changes in fish embryos measured by impedance spectroscopy after ultrasound treatment during exposure to cryoprotectant is reported here for the first time. The permittivity changes of zebrafish embryos in cryoprotectant solutions before and after ultrasound treatment were measured using impedance spectroscopy. Zebrafish (Danio rerio) embryos at 50% epiboly stage were exposed to 2 M methanol for 25 min before ultrasound treatment for 5 min at 22 degrees C. Embryos were treated with ultrasound in different frequencies (24 and 48 kHz) and voltages (50, 100, 150 and 175 V) combinations. The results showed a clear increasing trend of permittivity from voltage 50 to 175 V over lower impedance frequency range of 10-10(3) Hz indicating increased methanol penetration into the embryos after ultrasound treatment. The embryo survival was not compromised after ultrasound treatment under conditions used in the present study. The use of impedance spectroscopy technique provides a useful none-invasive tool for detecting changes of cryoprotectant penetration in fish embryos after ultrasound treatment. The technique is especially useful for the selection of the suitable cryoprotectants in embryo cryopreservation and may also allow quantitative measurements in embryo membrane permeability studies.     

Laboratory-scale ultrasound pre-treated digestion of sludge: Heat and energy balance

The objective of this work was to maximize the digestibility of biological sludge to elucidate the feasibility of a new sludge management strategy to recover good quality sludge for agricultural use. The combined effects of organic loading rates (from 0.7 to 2.8 g VS L⁻¹ d⁻¹) and the degree of disintegration by anaerobic digestion of sonicated activated sludge were discussed, and the thermal and energetic balances were evaluated. Despite low sonication inputs, sludge digestion performance improved in terms of solids degradation and biogas production depending on the soluble organic load. The biogas production by sonicated sludge was higher (up to 30%) with respect to the control. Filterability improved during digestion of sonicated sludge at medium OLR due to a significant abatement of the fines. Thermal balances indicated that sonication may be a proper system to guarantee self-sustaining WAS mesophilic digestion. Nevertheless, thickening is a pre-requisite to achieve a positive energy balance.     

Enhanced ROS production and cell death through combined photo- and sono-activation of conventional photosensitising drugs

A combination of light and ultrasound activation of two conventional photosensitising drugs, methylene blue and rose bengal, was shown to generate higher levels of reactive oxygen species (ROS) and lower LD50 values than either light or ultrasound activation alone.     

Transgenic expression of Angiopoietin 1 in the liver leads to changes in lymphatic and blood vessel architecture

To investigate the possible role of the Angiopoietins in vessel remodelling, we overexpressed one of the angiopoietins, Angiopoietin-1 (Ang1), in the hepatocytes of mice by means of the conditional binary transgenic system. Animals were examined by Doppler ultrasound, and dissected livers were analyzed by immunohistochemical staining. Double transgenic mice presented with enlarged spleens and kidneys, enlarged, disorganized blood vessels located near the surface of the liver, sprouting, dilation, and disorganization of liver lymphatics, and turbulent flow in about 1/4 of the blood vessels sampled. Most of these characteristics completely resolved within 12 weeks of turning off the expression of the Ang1 transgene, illustrating a dependence on the continual presence of Ang1 for maintenance of the vascular phenotype. Conditional Angiopoietin-1 overexpression in the liver of mice leads to a phenotype highly reminiscent of portal hypertension illustrating that Ang1 can drive both vascular and lymphatic vessel remodelling and may play a role in portal hypertension.     

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.     

Assessment of genome damage in occupational exposure to ionising radiation and ultrasound

The mutagenic effects of low doses of radiation on occupationally exposed subjects were studied on lymphocyte culture using two methods: analysis of structural chromosome aberrations and micronucleus assay. The results obtained in subjects exposed to ionising radiation alone were compared to those exposed to both ionising radiation and ultrasound. A correlation between the total number of chromosome aberrations and distribution of micronuclei in the genome of somatic cells show higher deviation in the group exposed to X-ray and ultrasound than in the group exposed to X-rays alone. The degree of genome damage in occupational exposure to X-rays and ultrasound were discussed.