Free radical formation induced by ultrasound and its effects on strand breaks in DNA of cultured FM3A cells.

Recent sonochemical studies have revealed that active oxygen species are formed by pyrolysis of water molecules due to high temperature cavitation bubbles. When aqueous solutions of DNA were sonicated, single-strand breaks and double-strand breaks of DNA were observed. Formation of double-strand breaks due to mechanical effects of cavitation and formation of single-strand breaks mostly due to free radicals were indicated. The sonochemically generated radicals from DNA constituents due to H atom and OH radical reactions, and pyrolysis processes, were identified by spin trapping with 3,5-dibromo-2,6-dideuterio-4-nitrosobenzene sulfonate. When suspensions of mouse mammary carcinoma FM3A cells and aqueous solutions of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were exposed to 1 MHz ultrasound in the presence of Ar, a good correlation between DMPO-OH formation and the cell killing induced by ultrasound were observed. Although single-strand breaks of DNA in the cells were observed at the maximum intensity of DMPO-OH formation and cell killing, double-strand breaks were not. Free radical formation by ultrasound in aqueous solutions and its relation to DNA strand breaks in vitro and in vivo are discussed.