Production of thymine base damage in ultrasound exposed EMT6 mouse mammary sarcoma cells

Abstract

Mouse mammary sarcoma cells, line EMT6 Ro, were exposed for 1 min to 1-MHz continuous wave ultrasound over a range of intensities from 0.5 to 30 W/cm2. The presence of thymine base damage products of the 5,6-dihydroxy-dihydrothymine type was determined by an alkali degradation assay. Production of damage was found to be greatest at an intensity of 10 W/cm2 and fell off rapidly above and below this intensity. Cells were also exposed for up to 5 rain at 5 W/cm2. A linear increase in thymine base damage was demonstrated with increasing time of exposure such that the rate of production at 5 min was approximately 4 times greater than that of a 1 min exposure. As a positive control, cells received absorbed doses of 60Co gamma rays up to 930 Gy. The amount of base damage produced at 10 W/cm2 ultrasound was approximately equivalent to a gamma ray absorbed dose of 177 Gy. Assay of cells immediately after sonication at 10 W/cm2 showed that approximately 14% of the cells had lysed. Survival data demonstrated that of the remaining unlysed cell population approximately 5% were viable, whereas cells exposed to 177 By showed no survival.

Book Review

“…28 After exclusions, the literature search on ultrasound's potential for damage to DNA resulted in 19 new papers being added to the database. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] Eighteen were level II evidence in which ultrasound was applied to in vitro collections of cells or DNA. The exception was a level III-2 paper that compared workers who had undergone long-term occupational ultrasound exposure to unexposed controls.…”

“…61 Overwhelmingly, in vitro studies demonstrate that insonication of liquids such as phosphate-buffered saline can produce reactive chemicals, particularly in the form of hydroxyl radicals or hydrogen peroxide, which in turn can result in DNA strand breaks and point mutations. [30][31][32][33][34][35][36][37][38][39][40][41][42]62 Apparently, strand breaks can also be induced by the mechanical forces produced by cavitation, although these are much more likely to occur in cells that have been lysed and are therefore unviable and have few long-term consequences. 36,[43][44][45] Strand breaks have been observed both in DNA unshielded by cellular membranes and nucleated DNA, at least some of which has been observed to occur in cells that remained viable after insonication.…”

Book Review

“…28 After exclusions, the literature search on ultrasound's potential for damage to DNA resulted in 19 new papers being added to the database. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] Eighteen were level II evidence in which ultrasound was applied to in vitro collections of cells or DNA. The exception was a level III-2 paper that compared workers who had undergone long-term occupational ultrasound exposure to unexposed controls.…”

“…61 Overwhelmingly, in vitro studies demonstrate that insonication of liquids such as phosphate-buffered saline can produce reactive chemicals, particularly in the form of hydroxyl radicals or hydrogen peroxide, which in turn can result in DNA strand breaks and point mutations. [30][31][32][33][34][35][36][37][38][39][40][41][42]62 Apparently, strand breaks can also be induced by the mechanical forces produced by cavitation, although these are much more likely to occur in cells that have been lysed and are therefore unviable and have few long-term consequences. 36,[43][44][45] Strand breaks have been observed both in DNA unshielded by cellular membranes and nucleated DNA, at least some of which has been observed to occur in cells that remained viable after insonication.…”

Method of cavitation-suppressed exposure of cells and explant mouse embryos to clinical real-time and pulsed Doppler ultrasound.

“…1 -5 Such concentrated thermal and mechanical events can cause the formation of free radicals ·OH and · H in aqueous solutions. 6 • 7 Dooley and coworkers 8 and Kondo and associates 9 have attributed in vitro biologic effects to such free radical formation. However, information available at present suggests that, if transient cavitation occurs in patients during exposure to diagnostic ultrasound, the events are rare, highly localized, and prob-embryos to the highest intensities of a real-time clinical ultrasound source with little possibility that significant temperature elevation occurs or that cavitation takes place in the medium surrounding the cells or embryos.…”