Transient permeabilization of cell membranes by ultrasound-exposed microbubbles is related to formation of hydrogen peroxide

Abstract

In the present study, we addressed the interactions among ultrasound, microbubbles, and living cells as well as consequent arising bioeffects. We specifically investigated whether hydrogen peroxide (H2O2) is involved in transient permeabilization of cell membranes in vitro after ultrasound exposure at low diagnostic power, in the presence of stable oscillating microbubbles, by measuring the generation of H2O2 and Ca2+ influx. Ultrasound, in the absence or presence of SonoVue microbubbles, was applied to H9c2 cells at 1.8 MHz with a mechanical index (MI) of 0.1 or 0.5 during 10 s. This was repeated every minute, for a total of five times. The production of H2O2 was measured intracellularly with CM-H2DCFDA. Cell membrane permeability was assessed by measuring real-time changes in intracellular Ca2+ concentration with fluo-4 using live-cell fluorescence microscopy. Ultrasound, in the presence of microbubbles, caused a significant increase in intracellular H2O2 at MI 0.1 of 50% and MI 0.5 of 110% compared with control ( P < 0.001). Furthermore, we found increases in intracellular Ca2+ levels at both MI 0.1 and MI 0.5 in the presence of microbubbles, which was not detected in the absence of extracellular Ca2+. In addition, in the presence of catalase, Ca2+ influx immediately following ultrasound exposure was completely blocked at MI 0.1 ( P < 0.01) and reduced by 50% at MI 0.5 ( P < 0.001). Finally, cell viability was not significantly affected, not even 24 h later. These results implicate a role for H2O2 in transient permeabilization of cell membranes induced by ultrasound-exposed microbubbles.