Uv-induced Dna Damage Model Study

DNA is an important biological macromolecule. The integrity of DNA is essential for cell or organism. Excessive ultraviolet radiation can cause damage in DNA, such as base pairs miss, DNA breakage, DNA-DNA cross-linking ,DNA-protein cross-linking, and chromosomal aberrations. If DNA damage can not be timely repaired, cell cancer or death would occur. Ultraviolet radiation (UV) with different energy lead to different DNA damage model, the repair mechanisms also may be not the same. Therefore, we study the DNA damage model induced by different energy UV. It has a certain practical significance for exploring DNA damage repair mechanisms and preventing some repair defective diseases.The effects of DNA damage induced by different waves and doses of ultraviolet radiation (UV) in different cells were tested by comet assay. The cell cycle distribution was detected by the flow cytometer (FCM). The effects of intermediate dose UVC on K562 cell was investigated by MTT test, cell count and comet assay. The effects of low dose UVC on K562 cell was investigated by DCFH-DA test and comet assay. The effects of high dose UVC on K562 cell was investigated by comet assay and atomic force microscopy (AFM).Results: 1. The primary cultured mouse hepatocyte and human leukemia K562 cells were irradiated by UVB or UVC with the same dose but different power. The experiment showed that the damage of DNA had no difference.2. The human leukemia K562 cells were irradiated by UVA, UVB and UVC. The experiment showed that UVA couldn't induce DNA damage immediately, while UVB and UVC could induce cellular DNA damage in a dose manner, and UVC could induce DNA damage most seriously. The relativity of UVB (20-320J/m~2) between DNA damage is 0.9344/0.956. The relativity of UVC (3.2-180J/m~2) between DNA damage is 0.9841/0.994.3. The sensitivities of different cells to UV were different. The lowest dose of UVC induced the human hepatoma SMMC-7721 cellular DNA damage was 10.4J/m~2, but the dose of UVC could induce DNA damage of h-hepatoma HepG2 cell was above 16.8J/m~2. The lowest dose of UVC induced mouse hepatoma hepal-6 cellular DNA damage was 1.6J/m~2, but for the primary cultured mouse hepatocyte was achieved to 2.4 J/m~2. The activated human lymphocyte was more sensitive than the resting human lymphocyte to UVC. 4. When synchronized K562 cells were irradiated by 60J/m~2 UVC, the cells of G2/M phase showed that it was more sensitive than others.5. K562 and the mouse hepatocyte cells were irradiated by low dose UVC, the DNA damage was detected by comet assay after incubated 2h but not immediately. Irradiated with low dose UVB or UVC, the intracellular ROS content increased, and decreased after the cells were incubated. The DNA damage of experimental group cell can be reduced by adding NAC.6. After irradiated by intermediate dose (60 J/m~2) UVC, the DNA damage of K562 cells represented delayed effect, and it can be repaired during 20h. Cell count and morphological observation showed that the number of K562 cells declined least after incubated 12h, and some cells damaged severely. The results of comet assay showed that the highest damage was appeared after incubated 2-4h. The cell cycle distribution was also changed after irradiated. Cells were arrested in Gl/S or G2/M.7. After irradiated by high dose UVC or UVB, the DNA damage model of DNA breakage and DNA cross-linking was highly appeared in K562 cells.Conclusions: The comet assay results showed that UVA couldn't induce DNA damage immediately, while UVB and UVC could induce cellular DNA damage in a dose dependent manner, and UVC could induce DNA damage most seriously. The linear equation of DNA damage and UVB: y=0.1196x-0.0534, R~2=0.9344 or y=0.0814x-0.0627, R~2=0.956. The linear equation of DNA damage and UVC: y=0.2018x+0.9053, R~2=0.9841或y=0.1251x+0.6914, R~2=0.994. The sensitivities to UV were different in different cells. The cancer cells were more sensitive to UV, and the sensitivity of cells to UV was related to its proliferation speed. When irradiated by lower dose UVC, DNA damage of K562 cell just appeared in a delayed manner, but not immediately. The delay was related to ROS. When irradiated intermediately by UVC (60 J/m~2), damage of the cell represented delayed effect, and it can be repaired during 20h. The cell cycle distribution was also changed after irradiating; cells were arrested in G1/S or G2/M. After irradiated by high dose UVC or UVB, the DNA damage mode of DNA breakage and DNA cross-linking was highly appeared in K562 cells.