Sonoporation‐Induced Apoptosis and Cell Cycle Arrest: Initial Findings

Sonoporation is known to be able to temporarily permeabilize cells, but during this process it may have traumatic impact on cell viability. In this work, we found that sonoporation may induce apoptosis and G(2)/M-phase cell cycle arrest in some cells hours after ultrasonic exposure in vitro. Methods: Suspensions of HL-60 leukemia cells were prepared (10(6) cells/ml), and a 1% v/v microbubble solution was added to induce sonoporation during ultrasound exposure. They were then placed 7cm away from a 2.54cm-diameter, 1MHz unfocused ultrasound probe, and these samples were insonated for 1 min with ultrasound pulses (10% duty cycle, 1kHz pulse repetition frequency). In this study, two levels of peak negative ultrasound pressure were used: 0.3MPa and 0.5MPa. After exposure, the cell suspensions were further incubated. They were harvested after 4h, 8h, 12h and 24h to analyze the cell-cycle distribution (sub-G(1), G(0)/G(1), S, G(2)/M) at these time points using propidium iodide staining and flow cytometry. Results: Some sonoporation-treated cells had undergone apoptosis by 4h, and the largest number of apoptotic cells (sub-G, phase) was observed after 12h (0.3 MPa group: 25.0%; 0.5 MPa group: 27.2%). Also, after experiencing sonoporation, some viable cells were stopped in the G(2)/M phase without undergoing cytokinesis, and the maximum G(2)/M population rise was seen after 12h (0.3 MPa group: +12.2%; 0.5 MPa group: +14.7%). This was accompanied by decreases in the populations of G(0)/G(1)-phase and S-phase.