Effect of ultrasound on DNA synthesis in tumor cells

Reactive oxygen species and DNA damage after ultrasound exposure

The aim of this work was to detect the formation of hydrogen peroxide and hydroxyl radicals after ultrasound (US) exposure and test the hypothesis that reactive oxygen species induced by ultrasound can contribute to DNA damage. Formation of reactive oxygen species was observed in incubated medium after sonication with 1 MHz continuous ultrasound at the intensities of 0.61-2.44 W/cm2. Free radicals and hydrogen peroxide produced by ultrasound exposure of cells can lead to DNA damage. Comet assay was used to assess the effect of ultrasound on the level of nuclear DNA damage. The nucleated erythrocytes from fish were exposed in vitro to ultrasound at the same intensities and frequency. It was noticed that ultrasound in all used intensities induced DNA damage. The effect was not eliminated by the addition of catalase, which indicates that DNA damage was not caused by hydrogen peroxide only. The results showed that the DNA damage can be repair and this mechanism was the most effective after 30 and 60 min after sonication. Furthermore, the ultrasound-induced DNA damage in the presence of sonosensitizer (Zn- and AlCl-phthalocyanine) was studied. It was noticed that phthalocyaniens (Pcs) alone or with ultrasound did not induce significant changes in the level of DNA damage.

Effects of dissolved gases and an echo contrast agent on apoptosis induced by ultrasound and its mechanism via the mitochondria-caspase pathway

Human histiocytic lymphoma U937 cells were exposed to continuous 1-MHz ultrasound (US) for therapeutic use, (0 approximately 6.5 W/cm(2) (I(SPTA)). Apoptosis and its related end points were examined by flow cytometry. Fraction of cells with low mitochondria membrane potential were observed after sonication and significant superoxide and peroxide formation, increased activity of caspase-3, and DNA fragmentation revealed biochemically, were also found. The fraction of early apoptosis and secondary necrosis increased with the incubation time after sonication. Early apoptosis observed at 6 h after sonication reached its maximum at 2 min of sonication and gradually decreased. On the other hand, secondary necrosis increased with the duration of sonication. When the effects of dissolved gases, Ar, N(2), O(2), air, N(2)O and CO(2), on free radical formation due to inertial cavitation were investigated by electron spin resonance (ESR) spin trapping, formation of hydroxyl radicals and hydrogen atoms was found in solutions saturated with Ar, N(2), O(2) and air, but not with N(2)O and CO(2). Apoptosis induced by US was also dependent on the dissolved gases in the order Ar = N(2) = O(2) = air >> N(2)O = CO(2) approximately 0. These results suggest that US-induced apoptosis, which is mitochondria-caspase dependent, was linked to inertial cavitation. However, quantities of free radicals did not influence the fraction of early apoptosis and secondary necrosis. When the cells were sonicated in the presence of an echo contrast agent, Levovist; synergistic enhancement of secondary necrosis induced by US was observed at concentrations of more than 20 mg/mL. In contrast, an additive increase of early apoptosis was observed in the combined treatments. These results suggest that Levovist; acting as cavitation nuclei, enhances secondary necrosis induced by US due to an increase in the membrane damage.

Ultrasound-assisted lipoplasty

BACKGROUND

Ultrasound-assisted lipoplasty (UAL) has been associated with particular types of complications and uncertain long-term effects arising from interactions between ultrasonic energy and living tissue. The present review seeks to address these issues.

METHODS

Search strategy Three search strategies were devised to retrieve literature from Medline, Current Contents, Embase and Cochrane Library databases up until April 2000. Study selection Inclusion of papers was largely determined using a predetermined protocol. English language papers were selected. Acceptable study designs included randomized controlled trials, controlled clinical trials, case series or case reports. Data collection and analysis Thirty-six papers met the inclusion criteria. They were tabulated and critically appraised in terms of methodology and design, outcomes, and the possible influence of bias, confounding and chance. Other papers were also included to provide background material.

RESULTS

There was little high-level evidence available comparing UAL and suction-assisted lipoplasty (SAL), with no conclusive evidence that UAL has a safety benefit, although low-quality evidence suggests that UAL is associated with reduced surgeon fatigue as well as increased operating times, slower aspiration rates and an increased learning curve. There is inadequate evidence to determine whether the theoretical potential for DNA damage from ultrasound is realized in the clinical setting.

CONCLUSIONS

The evidence base for UAL is inadequate to determine the procedure's safety and efficacy. The potential for DNA damage must be investigated with appropriate in vivo animal models. Recommendations for the safe use of UAL are discussed.

Biological effects of ultrasound: development of safety guidelines. Part I: personal histories

After the end of World War II, advances in ultrasound (US) technology brought improved possibilities for medical applications. The first major efforts in this direction were in the use of US to treat diseases. Medical studies were accompanied by experiments with laboratory animals and other model systems to investigate basic biological questions and to obtain better understanding of mechanisms. Also, improvements were made in methods for measuring and controlling acoustical quantities such as power, intensity and pressure. When diagnostic US became widely used, the scope of biological and physical studies was expanded to include conditions for addressing relevant safety matters. In this historical review, a major part of the story is told by 21 investigators who took part in it. Each was invited to prepare a brief personal account of his/her area(s) of research, emphasizing the "early days," but including later work, showing how late and early work are related, if possible, and including anecdotal material about mentors, colleagues, etc.

Ultrasonically induced alterations of cultured tumour cells

OBJECTIVE

The aim of this study was to establish: (i) which phase of the cell cycle is most sensitive to ultrasonic action; and (ii) whether and in which way ultrasound can influence components of the cytoskeleton.

METHODS

HeLa cell monolayers grown on glass cover-slips in DEM medium were used in all experiments. For proliferation studies, the cell monolayers were trypsinized and the cells were resuspended in fresh medium. The structure of the cytoskeleton was studied by means of the indirect immunofluorescence method. The cells were sonicated by a cw ultrasound of 0.8 MHz at low SA intensities (50, 100 and 500 mW/cm2) for 5 and 10 min.

RESULTS

The analysis of proliferation demonstrated that cells were most sensitive when undergoing M- and S-phases of the cell cycle. The ultrasonically induced disassembly of cytoskeleton components was most marked in microtubules and microfilaments due to depolymerization of basic proteins (tubulin and actin). The reaction of intermediate filaments was distinctly weaker.

CONCLUSIONS

In-vitro treatment of tumour cells with low intensity ultrasound results in partial inhibition of proliferation as well as in partial disassembly of all components of the cytoskeleton. Ultrasonically induced changes of the cytoskeleton seem to be non-specific and temporary.