Figure 5. Chromosome damage in human aortic endothelial cells as measured by the alkaline comet assay after exposure to radiation or after treatment with tumour necrosis factor(TNF). Cells exposed to 2 Gy or treated with 100 µM H₂O₂ were used as positive controls. Cells were treated with TNF at the indicated concentrations and trypsinized after 5 h for the comet assay. Nucleic acid was stained with SYBR Gold, and Komet 5.5 image analysis software was used to determine the percentage DNA in the comet tails of each cell examined. The data are presented as the average percentage tail DNA pooled from four separate experiments, and the p-values were determined by a two-sample t-test. Error bars represent the standard error of the mean (SEM). (a) TNF-exposed cells only with the indicated positive controls. (b) Cells were either treated as before or pretreated with 1000 units ml^–1 catalase for 1 h prior to the addition of TNF or exposure to X-rays or H₂O₂. (c) Cells were either treated as before or pretreated with both 150 µM pyrrolidine dithiocarbamate (PDTC) and 20 mM N-acetyl-L-cysteine (NAC) for 1 h prior to the addition of TNF or exposure to X-rays or H₂O₂.