The role of ultraviolet light in the induction of cellular DNA damage by a spark-gap lithotripter in vitro.

Abstract

The purpose of this study was to investigate the mechanisms for DNA damage induced by a spark-gap lithotripter. Cultured Chinese hamster ovary cells suspended in phosphate buffered saline were exposed in small chambers placed at the focus of a lithotripter in a 37C water bath. Viability was checked by trypan blue exclusion, and DNA strand breaks were evaluated with the comet assay after exposure. About 50% cell lysis and significant DNA damage in surviving cells were found after 500 discharges. The strand break effect, but not the lysis, could be eliminated by blocking the light emitted by the discharge. The exposure chamber material influenced the results, and use of nutrient medium with serum reduced the observed effects. The DNA damage was eliminated by added novobiocin and enhanced by added aphidicolin, as expected for strand breaks associated with repair of ultraviolet light damage. The DNA strand-break effect of 500 spark-gap discharges approximated that obtained from a positive control treatment with 38 J/m2. of 254 nm. ultraviolet light. Thus, the observed DNA damage appears to result from exposure of cells to the ultraviolet light emissions of the spark-gap discharge, rather than to the shockwaves or shockwave induced cavitation, which causes the cell lysis. Exposure of the skin to this ultraviolet light during lithotripsy might have some clinical implications for prolonged or repeated treatment.