The Generation of Stable Oxidative Stress-Resistant Phenotypes in Chinese Hamster Fibroblasts Chronically Exposed to Hydrogen Peroxide or Hyperoxia

With the recognition that chronic exposure to oxidative stress occurs in many disease states and can be deleterious to the human health, great interest has emerged in understanding the mechanisms by which mammalian cells develop resistance to chronic oxidative stress. In order to study the mechanisms of development of resistance to chronic oxidative stress, a model system where Chinese hamster fibroblasts (HA1) are chronically exposed to progressively increasing concentrations of H
2
O
2
(50–800 μM) or hyperoxia (80–95% O
2
) has been developed. Following >200 d of exposure to H
2
O
2
(or 18 months of exposure to hyperoxia), the cells developed stable H
2
O
2
-resistant (or O
2
-resistant) phenotypes that are characterized by increases in total glutathione, antioxidant enzyme activity, heme oxygenase activity, stress protein gene expression,
DNA
repair pathways, and resistance to a wide variety of other toxic stress known to cause oxidant injury. In addition, these oxidant-resistant cells exhibited amplification of the gene for catalase and constitutively elevated AP-1 DNA binding activity. Further, beyond 240 d genomic instability as evidenced by chromosomal rearrangements and alterations in ploidy was stably maintained upon removal from the chronic oxidative stress conditions. These results demonstrate the capability of mammalian cells to develop stable oxidative stress-resistant phenotypes in response to both exogenous (H
2
O
2
) as well as endogenous (95% O
2
) oxidative stress. The understanding of mechanisms of resistance to oxidative stress and its possible relevance in various disease states are discussed.