In vitro effects of 1‐MHz ultrasound on the mitotic spindle

Abstract

The effects of ultrasound on the cytoskeleton, comprising microtubules, had been studied decades ago. Nonetheless, very little attention has been paid to the effects of ultrasound on the mitotic spindle, which is also formed by microtubules. In this study, we treated human fibroblasts and human cancer cells (HeLa and MCF‐7) with 1‐MHz ultrasound at low intensities (70, 140, and 300 mW/cm2). In all cell lines, 5 min after the end of sonication, we found an intensity‐dependent increase of mitotic abnormalities (including multipolar spindles). Two hours after sonication, these abnormalities were present, but at much lower frequencies. Twenty‐four hours after sonication, mitotic abnormalities were at the same level of untreated samples, suggesting a transient effect due to ultrasound. Beside abnormalities of the mitotic spindle, we also observed an increase of metaphases with nonaligned chromosomes. The mitotic index of fibroblasts and HeLa cells, two hours after sonication, showed an intensity‐dependent decrease; this was not observed in MCF‐7 cells. In agreement with this last result, ultrasound‐induced growth inhibition (which was also intensity‐dependent) was more marked in fibroblasts and HeLa cells compared to MCF‐7 cells. This work indicates that therapeutic ultrasound, even at intensities below the cavitation threshold, can affect genome integrity, showing the need to increase the knowledge of the potential risks of ultrasound to human health. Environ. Mol. Mutagen. 2019. © 2019 Wiley Periodicals, Inc.

Biological Effects and Applications of Bulk and Surface Acoustic Waves on In Vitro Cultured Mammal Cells: New Insights

“…DNA double-strand breaks caused by these forces were evidenced in leukemic cells exposed to US at a 1 MHz frequency, with a 10% duty cycle, a 100 Hz pulsed wave, an intensity higher than 200 mW cm −2 , and an acoustic pressure of higher than 0.105 MPa [17]. Nevertheless, Udroiu et al demonstrated that US can affect the genome integrity even at intensities below the cavitation threshold [29]. Transient mitotic anomalies were observed after a 30 min US stimulation at 1 MHz, and an intensity of either 70, 140, or 300 mW cm −2 defined by the authors as, respectively, below, around, or over the cavitation threshold.…”