FIG. 15.

Redox homeostasis and strategies to modulate redox dynamics for potential therapeutic applications. Under physiologic conditions, normal cells maintain redox homeostasis by controlling the proper balance between ROS generation and elimination. The redox dynamics may fluctuate within a tolerable range. An increase of ROS may promote cell proliferation and survival, as in the case of many cancer cells. However, when the increase of ROS reaches a critical level (the threshold), it may overwhelm the cellular antioxidant capacity and trigger the cell-death process. Chronic ROS stress may cause accumulation of damage to a level that induces cell death. This is thought to be a mechanism contributing to neural degenerative diseases and aging. For therapeutic purposes, it is possible to use agents that promote ROS generation or inhibit the cellular antioxidant system to trigger cancer cell death by pushing the ROS above the threshold level. In contrast, antioxidants may be used to prevent cells from oxidative damage and delay aging and the neurodegenerative process.