Impact of thermal effects induced by ultrasound on viability of rat C6 glioma cells

• Published in: Ultrasonics Vol. 54; no. 5; pp. 1366 - 1372
• Main Authors: Kujawska, T., Secomski, W., Bilmin, K., Nowicki, A., Grieb, P.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-07-2014
• Subjects: Acoustic properties; Animals; Apoptosis; Assaying; Bursts; Cancer cells; Cell death; Cell Line, Tumor; Glioma - pathology; Glioma - therapy; In Vitro Techniques; Photo-sensitizers; Rats; Sonication; Sonodynamic therapy; Temperature; Thermal effects; Thresholds; Transducers; Tumor Cells, Cultured; Ultrasonic beam properties; Ultrasonic Therapy - methods; Ultrasound; Viability; Photo-sensitizers; Ultrasonic beam properties; Sonodynamic therapy; Cancer cells; Thermal effects
• ISSN: 0041-624X; 1874-9968
• DOI: 10.1016/j.ultras.2014.02.002

•Relationship between ultrasound energy delivered to a region of rat C6 glioma cells in vitro and their vitality was found.•Estimation of temperature rise induced in a region of the tested cells by HIFU depending on its acoustic properties was done.•Determination for each beam used the threshold exposure time that not induce thermal effects leading to cells death.•Demonstration that the thermal mechanism is crucial for viability of cancer cells treated by ultrasound.
In order to have consistent and repeatable effects of sonodynamic therapy (SDT) on various cancer cells or tissue lesions we should be able to control a delivered ultrasound energy and thermal effects induced. The objective of this study was to investigate viability of rat C6 glioma cells in vitro depending on the intensity of ultrasound in the region of cells and to determine the exposure time inducing temperature rise above 43°C, which is known to be toxic for cells. For measurements a planar piezoelectric transducer with a diameter of 20mm and a resonance frequency of 1.06MHz was used. The transducer generated tone bursts with 94μs duration, 0.4 duty-cycle and initial intensity ISATA (spatial averaged, temporal averaged) varied from 0.33W/cm2 to 8W/cm2 (average acoustic power varied from 1W to 24W). The rat C6 glioma cells were cultured on a bottom of wells in 12-well plates, incubated for 24h and then exposed to ultrasound with measured acoustic properties, inducing or causing no thermal effects leading to cell death. Cell viability rate was determined by MTT assay (a standard colorimetric assay for assessing cell viability) as the ratio of the optical densities of the group treated by ultrasound to the control group. Structural cellular changes and apoptosis estimation were observed under a microscope. Quantitative analysis of the obtained results allowed to determine the maximal exposure time that does not lead to the thermal effects above 43°C in the region of cells for each initial intensity of the tone bursts used as well as the threshold intensity causing cell death after 3min exposure to ultrasound due to thermal effects. The averaged threshold intensity was found to be about 5.7W/cm2.