Characterization of ultrasound-mediated cellular effects

Abstract

Ultrasound can temporarily make cells and tissue more permeable, an effect that could be used for enhanced and targeted drug delivery. Increased permeability is believed to involve creation of transient disruptions in cell membranes. This study seeks to characterize these disruptions and the mechanisms by which they are created, reseal and permit intracellular transport. To achieve this, DU145 prostate cancer cells were exposed to 24 kHz ultrasound with 0.1 s pulse length and 10% duty cycle for 2 s total exposure at pressures from 0.36 to 0.89 MPa. Disruptions were estimated to be at least 50 nm in diameter with lifetimes of 1–2 min using a range of fluorescent molecules with known molecular radii studied using flow cytometry. Cell morphological effects were examined using scanning electron, transmission electron, and laser scanning confocal microscopies after rapid fixation (within seconds after exposure). Images indicate that cell death from ultrasound exposure occurs due to a combination of apoptosis, necrosis and mechanical fragmentation and uptake may occur through physical disruptions in cell membrane structure. Using red blood cell ghosts and ATP-depleted prostate cancer cells, it was found that molecular uptake into viable cells requires active cellular processes which infers that cell recovery is an energy-dependent process.