| The role of oxygen as a damaging agent of DNA in a hybridoma cell line (HyHeL-10) was examined. Although oxygen is an essential nutrient for aerobic organisms, reactive oxygen species such as superoxide anion, hydrogen peroxide and hydroxyl radical are continuously produced as pan of normal metabolism. Aerobic cells possess antioxidant defense mechanisms, but these may be overwhelmed under stress conditions. DNA damage is of particular importance since DNA is the only molecule that is transmitted from one cell generation to another. Any modification of DNA due to, for instance, chemical damage caused by reactive oxygen species may modify the integrity of the genome. In this work, by using a sensitive fluorometric technique to measure DNA strand breaks, it is provided a clear experimental evidence that increasing dissolved oxygen (normobaric) in the culture medium, produces increased DNA strand breaks. It was also shown that in agreement with the observed DNA damage, the rate of production of intracellular reactive oxygen species increases as a function of the dissolved oxygen tension in the culture medium. It was also found that it is possible to compare the effects of both hyperoxia and hydrogen peroxide in terms of both the extent of DNA strand breaks and rates of change of intracellular reactive oxygen species. From mechanistic studies, a model based on a chemical Fenton-type of reaction was proposed to explain the induction of DNA strand breaks by oxygen. In this model, intracellular hydrogen peroxide can react with metal ions normally present in cells (such as copper and iron) generating hydroxyl radicals which cause the observed DNA damage measured in cells exposed to oxygen. Over the long term, cells subcultivated over an extended number of cell divisions experience a decay of DNA integrity probably due to the impairment of DNA repair capability. |
