Observation of DNA damage of human hepatoma cells irradiated by heavy ions using comet assay

Now many countries have developed cancer therapy with heavy ions, especially in GSI (Gesellschaft f r Schwerionenforschung mbH, Darmstadt, Germany), remarkable results have obtained, but due to the complexity of particle track structure, the basic theory still needs further researching. In this paper, the genotoxic effects of heavy ions irradiation on SMMC-7721 cells were measured using the single cell gel electrophoresis (comet assay). The information about the DNA damage made by other radiations such as X-ray, gamma-ray, UV and fast neutron irradiation is very plentiful, while little work have been done on the heavy ions so far. Hereby we tried to detect the reaction of liver cancer cells to heavy ion using comet assay, meanwhile to establish a database for clinic therapy of cancer with the heavy ions.

The human hepatoma cells were chosen as the test cell line irradiated by 80 Mev/u (20)Ne(10+) on HIRFL (China), the radiation-doses were 0, 0.5, 1, 2, 4 and 8 Gy, and then comet assay was used immediately to detect the DNA damages, 100-150 cells per dose-sample (30-50 cells were randomly observed at constant depth of the gel). The tail length and the quantity of the cells with the tail were put down. EXCEL was used for statistical analysis.

We obtained clear images by comet assay and found that SMMC-7721 cells were all damaged apparently from the dose 0.5 Gy to 8 Gy (t-test: P<0.001, vs control). The tail length and tail moment increased as the doses increased, and the number of cells with tails increased with increasing doses. When doses were higher than 2 Gy, nearly 100 % cells were damaged. Furthermore, both tail length and tail moment, showed linear equation.

From the clear comet assay images, our experiment proves comet assay can be used to measure DNA damages by heavy ions. Meanwhile DNA damages have a positive correlation with the dose changes of heavy ions and SMMC-7721 cells have a great radiosensitivity to (20)Ne(10+). Different reactions to the change of doses indicate that comet assay is a useful tool to detect DNA damage induced by heavy ions.