5-Aminolaevulinic acid enhances ultrasound-induced mitochondrial damage in K562 cells

Background

Ultrasound therapy is a new modality in the control of malignant cancers. The aim of the present study was to investigate the effect of 5-aminolaevulinic acid on the ultrasonic killing action in the cancer cells.

Materials/methods

The K562 cells as a cancer cell model were subjected to investigate the effect of 5-aminolaevulinic acid (5-ALA) on the ultrasonic killing action, in which the 5-ALA concentration was 2 mM and the ultrasound exposure was 15 s at the intensity of 0.46 W/cm² and the frequency of 1.7 MHz. Cytotoxicity was investigated 24 h after ultrasound exposure using the trypan blue exclusion test. Ultrastructural cell morphology and mitochondrial changes were observed using transmission electron microscopy (TEM). Mitochondrial membrane potential (ΔΨm) was evaluated using Rhodamine 123 assay.

Results

The death rates of the K562 cells in the controls including sham radiation and 5-ALA treatment alone were 1.81 ± 0.13%, 1.27 ± 0.20%, respectively. Those in ultrasound radiation alone and 5-ALA-ultrasound treatment were 12.61 ± 2.63%, 46.87 ± 4.09%, respectively. There were significant differences between 5-ALA-ultrasound treatment, ultrasound radiation alone and the controls (P < 0.05). TEM showed that the mitochondria expanding and some vacuoles were found in the ultrasound-treated cells. After the treatment of ultrasound and 5-ALA together some cells presented typical characteristics of apoptotic cells, such as nuclear condensation and crescent formation. Mitochondria of the cells were damaged more seriously than those treated by ultrasound alone, there were obvious swollen mitochondria and mitochondria in which cristae were almost perfectly disappeared, and more vacuolar mitochondria were founded. Mitochondrial membrane potential (ΔΨm) was more significantly collapsed when the K562 cells were exposed to 2 mM 5-ALA for 4 h and then 0.46 W/cm² irradiation of ultrasound than ultrasound radiation alone.

Conclusion

5-ALA pretreatment significantly enhanced the cytotoxicity of ultrasound radiation in K562 cells. The damage of mitochondria structure and function might be an important cause of cell death in K562 cells induced by the treatment of ultrasound radiation and 5-ALA together.