Induction of a bystander effect after therapeutic ultrasound exposure in human melanoma: In-vitro assay

Background: The induction of bystander effect via ionizing radiation has been well proven. However, few studies have investigated the bystander effect following non-ionizing radiation, such as ultrasound waves. Here, the bystander effect after different sonication times on human melanoma cell line (A375), is evaluated by assessing cell viability and apoptosis. Materials and Methods: The cells were divided into two main target and bystander groups. Target cells were exposed to 1 MHz ultrasound at 2 W/cm(2) intensity for 1, 2, 5 and 10 min with an ultrasound unit. Then, bystander cells received the cell culture medium of target cells. MTT and flow cytometry assays were used to determine the cell' viability at different times after exposure and medium transfer, as well as the detection of apoptosis. Results: The cell' viability in ultrasound-exposed target cells was less than 75% for 24 and 48 h incubation. Furthermore, bystander cell' viability was not significantly different from the control group 1 and 12 h after receiving the culture medium of target cells. However, bystander cells viability 24 and 48 h after target cells medium transfer was significantly decreased (P=0.01). The apoptosis rate of bystander cells, 24 and 48 h after receiving the cell culture medium of target cells, showed significant differences from the control group. Conclusion: This research results revealed that the ultrasound waves could induce a biological effect in A375 bystander cells which were not directly exposed to direct ultrasound.