甲醛对人Ⅱ型肺泡上皮细胞DNA氧化和甲基化水平的影响

目的：分析甲醛染毒对体外培养的人Ⅱ型肺泡上皮细胞(A549)内8-羟基鸟嘌呤脱氧核苷(8-oxo-dG)水平、DNA5-甲基胞嘧啶(5-mC)含量的影响及其时间-效应和剂量-效应关系，探讨甲醛所致的细胞DNA氧化与DNA甲基化的关联性。方法：用5～20μmol/L甲醛作用于A549细胞，用高压液相色谱串联电化学检测技术分析细胞DNA8-oxo-dG水平，用免疫荧光和高效毛细管电泳法检测细胞全基因组DNA5-mC含量改变。 结果：甲醛染毒提高了细胞8-oxo-dG水平，但是降低了细胞的DNA5-mC含量。甲醛致细胞DNA氧化与DNA甲基化呈现不同特点，A549细胞暴露于20 μmol/L 甲醛后，DNA氧化水平在1周甚至更早时间就已显著增高，而相同条件下DNA 甲基化水平的改变需要6周以上的时间，DNA 甲基化的改变滞后于DNA氧化。 A549细胞经5～20μmol/L甲醛染毒8周后，DNA氧化水平与甲醛剂量呈正相关关系，而同样条件下DNA甲基化水平与甲醛剂量呈负相关关系。 结论：甲醛染毒可提高DNA氧化水平，降低细胞DNA甲基化水平。在甲醛的毒作用效应中，细胞DNA氧化损伤可能是早于其DNA甲基化的一个重要分子事件。

DNA methylation and oxidation in human alveolar type epithelial cells induced by for maldehydeⅡ

OBJECTIVE： To explore the potential association of formaldehyde （FA）-induced cellular DNA oxidation and DNA methylation. 8-oxo-7,8-dihydroguanine （8-oxo-dG） levels and DNA 5-mC content were analyzed after FA exposure in human alveolar typeⅡepithelial （A549） cells in vitro,and their time-dose-effect were also analyzed. METHODS：A549 cells were exposed to 5-20μmol/L FA. 8-oxo-dG levels of cellular DNA were measured by high pressure liquid chromatography with electrochemical detection,alterations of genomic DNA methylation levels were investigated by immunofluorescence and high performance capillary electrophoresis. RESULTS：The levels of 8-oxo-dG in A549 cells were increased after FA exposure,but cellular DNA 5-mC content is reduced. There were different characteristics in FA -induced cellular DNA oxidation and DNA methylation. After exposure to 20 μmol/L FA, DNA oxidation levels of A549 cells had increased significantly in 1 week and even earlier. However,it took at least 6 weeks for significant changes in the level of DNA methylation under the same conditions. After exposed to 5-20μmol/L FA for 8 weeks,a positive correlation was found between the dose of FA and DNA oxidation levels in A549 cells,but the DNA methylation levels were negatively correlated with the dose of FA under the same conditions. CONCLUSION：After FA exposure,oxidative DNA damage in A549 cells was increased but DNA methylation decreased. In the cytotoxicity effect of FA,oxidative DNA damage might be an earlier important molecular event than DNA methylation.