Nitric oxide-induced resistance to hydrogen peroxide stress is a glutamate cysteine ligase activity-dependent process

Nitric oxide (^.NO) is a reactive nitrogen species known to be involved in cytotoxic processes. Cells respond to cytotoxic injury by stress response induction leading to the development of cellular resistance. This report describes an ^.NO-induced stress response in Chinese hamster fibroblasts (HA1), which leads to glutathione synthesis-dependent resistance to H₂O₂-mediated oxidative stress. The development of resistance to H₂O₂ was completely abolished by the inhibition of glutamate cysteine ligase (GCL) during the first 8 h of recovery after ^.NO exposure. Altered thiol metabolism was observed immediately after ^.NO exposure as demonstrated by up to 75% decrease in intracellular thiol pools (glutathione, γ-glutamylcysteine, and cysteine), which then reaccumulated during the ^.NO-mediated development of resistance. Immunoreactive protein and activity associated with GCL decreased immediately after exposure to ^.NO and then reaccumulated during the development of resistance to H₂O₂ challenge. Moreover, compared to N₂ controls the activity levels of GCL in ^.NO-exposed cells increased approximately twofold 24 h after H ₂O₂ challenge. These results demonstrate that ^.NO exposure is capable of inducing an adaptive response to H ₂O₂-mediated oxidative stress in mammalian cells, which involves alterations in thiol metabolism and is dependent upon glutathione synthesis and increased GCL activity.