Low-frequency ultrasound induces apoptosis of rat aortic smooth muscle cells (A7r5) via the intrinsic apoptotic pathway.

Ultrasound, a non-invasive therapy method, is a potential tool for medical applications, but its biological effects on vascular smooth muscle cells (VSMCs) have not been characterized. The aim of this study was to explore the effect and possible apoptotic mechanism of VSMCs that were induced by low-frequency ultrasound (LFU). Cell viability and apoptosis of A7r5 cells were evaluated after treating A7r5 cells with a continuous 45-kHz 1.0-W/cm(2) ultrasound (exposure time of 0, 10, 20, 30, and 35 s) by MTT assay and flow cytometry. At the optimum ultrasound exposure condition (30 s), gene chip analysis was performed, and the apoptotic signaling pathway was confirmed by reverse transcription-polymerase chain reaction and Western blot. As measured by flow cytometry, LFU significantly induced A7r5 cell apoptosis. Comparing the ultrasound group with the control group, the protein expression of caspase-9 and caspase-3 was increased by 50 and 57%, respectively; the caspase-3 mRNA level was increased by 37.5%. These findings indicate that an intrinsic pathway plays a major role in apoptosis that is induced by LFU and that LFU can induce A7r5 cell apoptosis via caspase-9- and caspase-3-dependent pathways.