Cellular Pre-Adaptation to the High O 2 Concentration Used in Standard Cell Culture Confers Resistance to Subsequent H 2 O 2 -Induced Cell Death.

The addition of hydrogen peroxide (H 2 O 2 ) to cultured cells is widely used as a method to modulate redox-regulated cellular pathways, including the induction of programmed cell death in cell culture experiments and the testing of pro- and antioxidant compounds. Here, we assessed the effect on the cellular response to H 2 O 2 of pre-adapting squamous cell carcinoma cells (A431) to the standard cell culture oxygenation of 18.6% O 2 , compared to cells pre-adapted to a physiological skin O 2 concentration (3.0% O 2 ). We showed that cells pre-adapted to 18.6% O 2 resisted H 2 O 2 -induced cell death compared to cells pre-adapted to 3.0% O 2 for 96 h prior to treatment with H 2 O 2 . Moreover, the enzymatic activities of catalase and glutathione reductase, as well as the protein expression levels of catalase, were higher in cells pre-adapted to 18.6% O 2 compared to cells pre-adapted to 3.0% O 2. H 2 O 2 -resistant cells, pre-adapted to 18.6% O 2 , exhibited increased nuclear Nrf-2 levels. It is concluded that A431 cells pre-adapted to standard cell culture oxygenation conditions resist H 2 O 2 -induced cell death. This effect may be related to their heightened activation of Nrf-2.