Effects of dissolved gases and an echo contrast agent on ultrasound mediated in vitro gene transfection

The effects of acoustic cavitation on in vitro transfection by ultrasound were investigated. HeLa cells were exposed to 1.0 MHz continuous ultrasound in culture media containing the luciferase gene. Transfection efficiency was elevated when an echo contrast agent, Levovist was added or air was dissolved in the medium. When cells were sonicated in medium saturated with Ar, N2 or N2O which have different γ values (Cp/Cv), or were saturated with He, Ar or Ne with different thermal conductivities, the effectiveness for the dissolved gases in the ultrasound mediated transfection was Ar>N2>N2O or Ar>Ne>He, respectively. When free radical formation in water by ultrasound was monitored as a measure of inertial cavitation, it was similarly affected by dissolved gases. These results indicate that the efficiency of ultrasound mediated transfection was significantly affected either by occurrence of or by modification of inertial cavitation due to various gases.