Observations on the viability of C6-glioma cells after sonoporation with low-intensity ultrasound and microbubbles.

Ultrasound (US) and microbubbles can be used to facilitate cellular uptake of drugs through a cavitationinduced enhancement of cell membrane permeability. The mechanism is, however, still incompletely understood. A direct contact between microbubbles and cell membrane is thought to be essential to create membrane perturbations lasting from seconds to minutes after US exposure of the cells. A recent study showed that the effect may even last up to 8 h after cavitation (with residual permeability up to 24 h after cavitation). In view of possible membrane damage, the purpose of this study was to further investigate the evolution of cell viability in the range of the 24-h temporal window. Furthermore, a description of the functional changes in tumor cells after US exposure was initiated to obtain a better understanding of the mechanism of membrane perturbation after sonication with microbubbles. Our results suggest that US does not reduce cell viability up to 24 h post-exposure. However, a perturbation of the entire cell population exposed to US was observed in terms of enzymatic activity and characteristics of the mitochondrial membrane. Furthermore, we demonstrated that US cavitation induces a transient loss of cell membrane asymmetry, resulting in phosphatidylserine exposure in the outer leaflet of the cell membrane.