Ultrasonic cavitation indirectly induces single strand breaks in DNA of viable cells in vitro by the action of residual hydrogen peroxide

Abstract

Direct exposure of cells to vigorous ultrasonic cavitation results predominantly in mechanical cell lysis, but latent effects due to production of toxic sonochemicals can also be present. Phosphate buffered saline (PBS) was exposed to 1.61 MHz ultrasonic cavitation at 20°C in a rotating tube exposure system to build up sonochemical products. Single strand DNA breaks (SSBs) were then induced by treating Chinese hamster ovary (CHO) cells with the cavitated PBS for 30 min on ice. The SSBs resided in viable cells, as evidenced by their ability to repair the breaks when warmed. This indirect effect could be explained by the action of cavitation-generated hydrogen peroxide that had built up (e.g., to 16 μM after 30 min exposure) in the PBS. Dissolution of argon gas in the PBS before exposure enhanced the SSB effect and the H202 production. Addition of catalase to the cavitated PBS before cell treatment eliminated the H 2O 2 and the SSB effect. Tests with hydrogen peroxide showed that 16 μM H 2O 2 treatment for 30 min on ice was as effective as a 1 Gy dose of 60Co gamma rays in producing single strand breaks. The SSB effect of H 2O 2 and gamma rays was reduced by addition of the radical scavenger cysteamine to the cells before treatment, but cysteamine did not reduce the SSB effect of direct exposure to ultrasonic cavitation. These results help to clarify the potential for genetic effects from ultrasonic cavitation.