Oxidative DNA damage in human respiratory tract epithelial cells. Time course in relation to DNA strand breakage

When human respiratory tract epithelial cells were exposed to 100 μM H₂O₂, there was rapid induction of DNA strand breakage and chemical modifications to all 4 DNA bases suggestive of attack by OH(̇). The major products were FAPy-adenine, FAPy-guanine, and 8-OH-guanine. Some of the base modifications were removed very quickly from the DNA (e.g., 8-OH-guanine), whereas others persisted for longer (e.g., thymine glycol), probably due to differential activity of different repair enzymes. By contrast, strand breaks continued to increase over the rime course of the experiment, perhaps because strand breakage is also implicated in the repair process. One should therefore be cautious in using strand breakage as a sole measure of oxidative DNA damage, and when drawing conclusions about the pattern and biological significance of oxidative DNA damage in cells the relative persistence of different lesions must be considered.